My suggestion is to never buy one without checking with the mfgr first. That's the only way you're going to know if it's been back to the mfgr for being flooded, etc, and the mfgr will have any work record on the unit. It's a good way to create a relationship with the mfgr, too.
Also, the mfgr will usually know of units that will be coming on the market before anyone else knows about them, or may have taken one in on a trade they will sell you. Huge advantages of buying a unit from the mfgr, too, as they will have gone over it carefully.
Obviously the forums work. Put out a wanted to buy notice if you don't see one for sale.
I've been driving one for 10 years and can tell you that: 1. your 1st probably won't be your last, 2. spend the money to get a good "dependable" unit (the longer you own it the less it cost per year), 3. send a used one to the mfgr for a going over (you just need to ship the motor and prop unit to save size & weight).
Good luck.