I've got 4 of these puppies, and I'll tell you, if I had more electricity and could handle more heat in my bedroom, I would. (My room runs a bit hot, gotta have a fan on me).
Buying from bitmain is the best deal, but a third party will still be profitable at certain prices.
Tips for buying miners second hand:
First - Make sure you calculate the value using bitcoinwisdom's difficulty calculator, at minimum 1 month should look to earn you 50% of your money (because the difficulty will go up and this isn't factored in there).
Next, before picking it up or having it delivered, request 20min of the miner configured to your pool to verify the gh/s rate, you don't want faulty hardware.
Lastly, find out whether or not it comes with a power supply, this should be factored into the value decision. You'll want 500w+ for one miner just to be safe.
What does this have to do with the proposed vs. actual wattage of an Antminer S1?