I'm with Adam; first and foremost is the breeders benefit in this transaction, and if these animals are selling without payment plans, i woudl sell them that way as well. I personally HATE payment plans, been screwed too many times to count, so the only ones that I now offer are a 25% (very firm) non-refundable deposit with the remainder to be paid off in two payments no longer than three months.
If you don't like the terms of payments plans, save up and buy the animal outright. Cash is still king.