You will get the estimate to the penny as long as what you described is exactly what they receive...if you have scratches but you claim no scratches (and keep in mind they detailedly ask about light scratches), you'll get a bit less than what was offered...this will incrementally go down with the different questions if you answer dishonestly.
That said...you'd have to be some kind of desperate fool to take $285 for the iPhone 4S. You can sell your iPhone 4S 16GB in perfect condition right now on eBay for around $400. It will sell almost immediately, and if you have an unlocked version, expect even higher profit. I don't know about you, but I'm not ready to throw nearly $100+ away for the sake of convenience (which still really doesn't make sense because you still have to ship it off and you have to wait for them to review your product before you get the credit).
And one last thing...the company that runs that program is not Apple, it's a company called PowerON (which does all kinds of consumer electronics recycling). Just thought some people might want to know that since im guessing the idea that Apple some how is controlling this recycling program might make some people more inclined to do it, when essentially, you're just working with a 3rd party, and might as well sell it for what it's actually worth.