I bought a Merc 5hp 4s from Academy 18 mos ago, full factory warranty, came in a sealed factory carton, etc. with all owners manuals/info, yada yada yada. Just make sure the shipping carton is still sealed so you have a better assurance that all the info and parts are there.
I had trouble with the 5 being hard to start when cold, it would flood out, etc., so I took to the local Merc dealer here in town. When they asked if I bought it there and told 'em no, I could tell they did not really want to work on it but did (warranty work) and they fixed it, they had to drill out the brass plug to make some fuel flow adjustments. It runs fine now, and starts much easier. You will/might save a couple hundred bucks. Might want to check out BPS, they have some pretty good deals on Mercs at times, like $500 off or more on the smaller OB's.