If you are in the US, you pay their taxes on their commission ...

That's not entirely true.

A) You don't pay their taxes. It's not possible to pay somebody elses taxes. Well, you could physically pay their tax bill, or give them the money for their tax bill... but you will never be held responsible for taxes that aren't your responsibility to pay. So the only way you could be paying their taxes is if the withheld money is actually being used by Envato's taxes rather than your taxes. If that was happening, it would be easily found out (and would have been found out by now), and would result in massive fines and possible jail time. I don't think they're that stupid.

B) If I pay more tax than I should, in relation to a transaction, it doesn't mean somebody else can pay less. Like if VAT is 20% and I charge someone 40% instead, I can't use that extra 20% to reduce the amount of income tax I have to pay on that sale. If Envato is getting $4 from an $8 sale then they can have the most complicated fee, commission or tax structure in the world... but that full $4 is still going to have to show up on their tax return as revenue. 

C) When submitting a tax return, Envato will provide you with a document every year stating the amount of tax that has been withheld. If you're in the US, or any country that has a double taxation treaty with the US... then you can use that amount to offset the tax due in your country.

The only thing that really put my off, was that they'll own them forever. Well, they don't own them... you still own the rights to them and are welcome to sell them elsewhere... but I was imagining the unlikely scenario of somebody offering my millions of dollars for exclusive rights to my entire portfolio. I wouldn't be able to include those as there would be a limitation on where they could upload... i.e. not VideoBlocks. An unlikely situation, but still... you never know what might happen in one, two, five, ten years. That was my main concern. Other than that, with the ability to exclude your best selling clips, I couldn't really see any down sides.

In the past we too tried uploading stock files to many agencies... but we started to delete everywhere where we rarely get sales. It's waste of time uploading if it's not profitable.

Is it just me, or is it slightly ironic that you attempted to avoid wasting time doing things that aren't profitable, by actually wasting time doing something that isn't profitable in the slightest (deleting files)? Keeping them where they are might bring in a tiny bit of revenue, no matter how small... deleting them is guaranteed to not bring you in any revenue.

I had the same, but they took 50 clips. The key for me was you can choose which clips you don't want included. If they chose my 50 best clips, then on a good month, I'll be in the red for a few months and then I'll lose out. As I nominated my ten best selling clips not to be included... it'll be a couple of years before I'm losing out... so that made it a much better option.

This bookshop is...

You did quote earnings after tax, as you're saying that $2,300 is the same as earning $3,300 when you take taxes into account. When you take taxes into account its less than $2,300... not higher.

Yeah but nobody quotes earnings after tax. The $2,300 you mention is the minimum wage... which is before any taxes, so if you get $2,300 left from $3,300... then using the same maths, $2,300 is actually $1,602. So $3,300 being the same as $2,300 doesn't work... as you're comparing them differently.   

(It won't be $1,602, as I'm assuming Australia has some kind of minimum earnings threshold like most countries [so that amount will be higher]... but still, I'm just going on the data in this thread)

As far as I'm aware, most published average or median wages are calculated without tax included. As you say... taxes are going to vary widely depending on where you live, so a comparison of amounts before tax would make more sense.
 

Just a couple more questions. The agencies listed on the Black Box website... are those all of the sites they submit to, or are there more? And if I have all of my content on, for example, just one of the sites listed... does that mean there's no point? Or if there are sites on there that I don;t have any content on, can it be submitted just to those?

For example... I don't have anything on Dissolve. So would my content be accepted there, even though I have that same content on VideoBlocks, Pond5 etc?

These answers relate purely to video...

a) What is your portfolio size?

About 550 give or take.

b) What average monthly earnings (USD) have you seen over the last 12 months?

$3,300

c) Any specific sites you recommend? (I do see the list on the right, I'm asking about you personally what worked best for you).

Pond5, Shutterstock, VideoBlocks, iStock and VideoHive are my five best earners. They're not specifically 'recommendations' though.

d) Any trends/things you'd recommend focusing on? (I.e., certain types of video/styles/etc?)

From my experience, motion graphics work sells better than live action video. It also takes more time, so the key is to find a way to make decent quality stuff quickly. Hybrid shots might be an idea... live action hand holding an animation of the Earth etc. They're pretty common, but I'm sure you could come up with something more unique.

Sure, it's a well known brand name, but nobody has heard of Kodak Stock, or whoever it is. It's an untried and untested agency, so although the brand name will no doubt entice some people to dip their toes in the water... it's not like everyone is going to ditch SS, iS and all the other sites the moment they open their doors.

One thing to note, before the pitchforks come out... animation does a lot better at VideoHive than live action content, so unless you're doing motion graphics, then it's unlikely VideoHive will be at the top of your list when it comes to sales figures. Combine that with the low prices and the current queue length, and most people aren't too keen on them, which I guess is understandable. However, the queue is slowly coming down, and within the next few months you'll be able to set your own prices. And there's a good volume of sales as well... I guess the lower prices mean people are just buying more.   

I only do video, but I signed up there nearly two years ago... and haven't sold a single thing. I get hundreds of sales a month, so you think I'd get at least one there over a period of two years! Then again, it is called deposit-photos rather than deposit-videos, and it's in the middle tier on the right, so might be worth it for your images. Not sure about the whole signing up/submission situation.

You get paid with KodakCoin you convert it to your local currency, you don't sit on it.

How do I convert it? Obvioulsy it's new, so nobody knows exactly... but say they were paying in Bitcoin instead.