Honestly if this seller has had this animal for a while and the health card is clean and free of disease, I doubt you'll have any issues.
The "stories" of the WC nightmares also go hand in hand with the early caging and husbandry practices. There have been so many advances in care that can lead to success when acquiring a WC animal.
Couple that with the fact you have a rather well established animal that is not a fresh captive and I see no reason you'd have issues.
Just be vigilant about the transition and care early on, and I doubt you'll have issues.
I'm looking forward to photos as I think WC animals have the most beautiful "Mother Nature" paint jobs there around.