MicrostockGroup

Care to expand on this?  What does "collaborate with each-other" mean?

Eavesdrop at a conference... People talk... be the wall with ears
j/k, mostly

It's most-often not a 'formal' collaboration, but negotiating with agencies is common-place and photographers know that distributing their work together (as a network) is a great way to demand higher prices. Monkey business run just such a network for at least a handful of the top-20.
Along with the top 100-or-so photographers clearly visible in iStock's search results (just look at page 1/2 of any search). Their results are clearly split between top contributors and partner/sponsor programmes at almost any agency (iStock is leading the way here of course, but the same can be seen at any agency with funds to spend on their search algorithm).

I'll confirm what Bob is saying. Search placement would seems to be something thats on the table. That is if you have a big Port with good selling power.

Are you saying IS offered you something to not go independent?

The search-placement issue has been discussed many times on microstockgroup and was demonstrated perfectly in Rahul's post on the Lookstat blog so I won't get into it (as it's a waste of everyone's time). It's a fact that if you produce images that convert views into sales, you will get more impressions... (this seems to be a universal truth of online-sales of pretty-much anything) the top contributors DO produce images which sell... ergo... top contributors get more impressions. Don't waste your own time or energy believing otherwise.

Edit: I don't refer specifically to iStock, all big agencies do this, some of the through negotiation, some through performance. In iStock's case, the only thing I know which they don't flex on is upload limits (even Yuri has the normal limit), afaik everything else would be up for discussion with the right portfolio (though with the current market-pressures you'd have to take them an awesome footage portfolio to get much give at the moment)

No! What I'm saying is that after talking with some top producers search placement is indeed something that is negotiable.

I don´t know nothing about IS but I do know (and everyone else can check) that DepositPhotos have made a few top contributors into their highest ranking without selling what is supposed to

Dammit!

If search placement is "negotioable on istock" means deals along the lines of "We promise to put x% of your files into Vetta/agency" then yes, I will believe that, because this is already being done with all that content coming in from Getty. V/A gets preferential treatment in the search. So do the exclusive files and aren´t there a few Getty artists/groups that have exclusive crowns although they are not exclusive and also sell their files elsewhere?

But for the normal collections? I do a lot of searches, really a lot on istock and I have never seen anything that would make me believe that some contributors had "special deals" to push their content to the front.

Besides, we all know the joke how if it wasn´t programmed by Sean the code wouldn´t work and mess up the site...and there is truth to that.

Let's not be naive.  Every business arrangement is negotiable. 

None of this should surprise anyone... we don't live in a fair world, so why would anyone expect anything other than preferential treatment and favoritism to exist?  Favoritism goes to those that bring a lot to the table.  I've seen it happen so many times; even intercepted a few emails I was CC-ed on by mistake, which give proof of it. 

Yes I tend to think you are perfectly correct with that belief.