I  think you're being paranoid.  A good shot, straight out the camera, with no added sharpening will be accepted at all the agencies.  You should never sharpen.  Reviewers know that images look slightly soft at 100%.  If you are getting lots of these rejections it may be time to review your technique, or do a few lens tests to check the focus.

For SS, since there's no difference in royalties based on size, I just find it easier to downres if something gets rejected for focus.

Part of the issue of SS to me seems the reviewers don't get selective focus.  If the center area where they default zoom isn't sharp, they seem to reject the whole thing, even when a different area is meant to be the sharpest.

IMO 50mm lenses are usually excellent value for money, that is not perfect but for the price a very good performer.   If you are talking a sigma / tamron 70-300 (which is another good value for money lens but usually not spectacular) you're 50mm should be significantly better.  I have some beautiful glass ie voigtlander 125 & 180's but I also have plenty of shots accepted from a 35-135mm zoom that cost $20 from the pawn shop

I have shots that are technically perfect, but boring get rejected while shots that I know are a bit noisy or not so perfect get accepted because they are 'good shots' (well I think they are

as for sharpening I leave lightroom on default sharpening,  I usually do a little hiroloam sharpen (between 8-15) and then if needed (often for my taste) I high pass sharpen anywhere between 0.5 and 1.2 depending on the image and subject, and I often use masks to just hit specific points.   So basically I do the first 2 stages.  Capture sharpen and then gentle creative sharp but leaving the final sharpening for the purchaser.  Doing it this way I never get oversharpened

Phil

Sharply pretty much nailed it.

Regarding sharpening...I don't.  My favorite sharpening plugin is Fred Miranda's Intellisharpen II.  It is great for my sports photography which is not intended for stock usage.  However despite its claims, it indeed introduces artifacts and halo (even with 0 halo chosen).  These things were not clear to me when I first started shooting stock.  Now they are obvious.  The effects of sharpening ruin the image in my eyes, when it comes to producing nice, clean stock.

Sure, images have to be technically good in order to be accepted

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This would be the crux of my problem.  Sans having a studio to do any studio work or a model to do any shots with humans, I have been relying on shots out and around the town to this point ( ) or limited stuff that is possible with a single off camera flash (I figured out some great ways to fake a fancy studio with PS with multiple exposures and an off camera flash, but several hours of PP work per shot is way too inefficient to be reasonable).  I don't have a problem getting the studio type stuff accepted, but my setup is way too inefficient to do much with (very creatively stifling as well, all the creativity goes into faking proper lighting), but that will change shortly, I've got some studio lights on the way, so I can begin to act on my little black book full of ideas that has been filling up but has little checked off the list.

The meterstick thing is a means to test the focusing of your lenses (response to the first reply), tilt a meterstick, aim at the 18" mark with the camera on a tripod from about 5-8 ft away, let it AF with the lens wide open and take a shot.  If it is focusing correctly the 18" will be sharp, other #'s will be blurry, if it has front focus or backfocus problems a different # will be sharp.  I learned this with my first lens, which was a Sigma 18-200.  Darn thing could not take a sharp shot.  Checked it on the stick and it had a severe backfocus problem.   I didn't want to go through the hoopla of getting it fixed so I returned it and got a Canon lens (2 actually).  First thing I did with those is check them too to make sure the focus was correct.  Both were perfect.  My 70-300 is a Canon not Sigma or Tamron (I'll probably never get another 3rd party lens after the first Sigma incident).  I learned right away that some of the first shots with a new lens (especially an internet purchase) should be to test its focus, and this is a quick and easy way.

My 50mm though, taken straight on at a wall from 10 ft away on a tripod will be pure blur in the corners (RH side much worse than the left) and sharp in the center at less than f/5.6, so bad that all shots at less than f/5.6 have been rejected for focus.  Every landscape shot that I have taken has been rejected for this (landscapes are tough, the degree of technical perfection must be higher than a great idea in a studio).  I typically shoot landscapes when the sun is getting low, I can HH a 1/60 f/3.5 shot fine, but they will all be rejected for the corners.  I'll post some little example 100% crops of this and my red bleed later (I need to check if it is an ACR problem causing the bleed, might not be present if I use Canon's program).  I get the feeling though my 50mm is just a bad copy, heck it is an $80 lens, can't expect them all to be perfect, just have to stick to isolations with it until I upgrade, I'll have a superwide for the landscapes in not too long anyway.

The question that prompted the thread though has been answered.  Skip the sharpening.

How do you get past shadows and the directional light of a flash?  Even bounced a flash leaves bad shadows (my current (soon to be obsolete) setup is a white sheet attached to a wall draped over a small glass top end table with attached white sides and a very low ceiling (the top almost touches it)).  If the object needs front light, the shadows are bad in the back, from above the shadows are bad in the front (plus the underside of objects are heavily shaded).  I shoot with the remote release on the tripod, move the flash around, then combine several exposures into one with layer masks and blending modes.  I get good results, but it is very tedious.

I'm switching to 2 strobes with modeling lights with a few light control means (umbrellas, softboxes, barndoors, grid) (really didn't cost too much either, they're fairly low power, cheaper than a 580 flash), dropping the sides on the setup, hanging the sheet from a curtain rod and getting a few other fabrics, and moving my flash under the table for isolations (goodbye shadows).  I'll be able to take my camera off the tripod and HH it so I can move around and take less sterile pictures, plus I'll have the light and space to do so much more.  Heck I've got the space, I've got an unused finished attic just waiting to be used for something (my studio).  Most of my ideas just aren't possible or are very difficult to pull off good with a single flash and camera tied to a tripod.  I've spent hours pondering how to pull off some shots, even then it is iffy so I haven't tried with the more challenging stuff (and failed on a few things to get results that I liked).  I always came to the same conclusion...if I only had proper lights and a less restrictive space.

Would you use your big strobes if they were always set up and you had a dedicated studio?  Just takes a little repositioning (maybe, I figure there would be a standard small object isolation layout).  Then again, I don't have a huge amount of interest in just finding small objects around the house and isolating them, though a white or black background is key for most of my ideas.