Hi,
If they are bad at customer service before the sale, wait till after... i would avoid that!
Best time will be coming up soon. When females have laid their eggs and breeders are replacing them with something else. I would suggest getting an animal in the 800- 1100 gram range though since most people only sell adult breeders if they have low egg production (4-5 eggs on a big female) or something wrong. You may get lucky and find someone getting out of breeding...?

Ask a LOT of questions before you buy.
1.Age (important! you dont want an overfeed yearling)
2.Feeding
3.Egg production (if proven)
4.What were they breed to last (they can retain sperm)
etc...

Good luck!
Jon