I first try to buy locally. That's usually not an option anymore though. Then I try to buy from DanO or George. That is usually a good option. My current SD1 came slightly used from DanO. Good price, good service. While I still haven't bought much from George, I have referred several local buyers to him and also some to DanO. Everybody is pleased with both of them.
I usually buy a keyboard about once a year. I've determined not to buy anything I can't personally audition, so that lets out several of the top-end models. I also won't buy anything extremely heavy (over around 35 lbs).
The right to return within 60 days may well be a factor in future purchases.
DonM