make sure to buy and read a book about rays so that you are well informed when you are ready to buy. Freshwater stingrays publ by Barrons by Dr Richard Ross is a good deal for $8 )
Sadly some of the sellers on the forums are not as informed as they like to pretend and often will sell skinny and/or sick rays wrongly identified etc.
also ask about any guarantees offered and for photos of the actual ray you might buy so you can see if it at least looks fat and healthy.
ask lots of questions on the forum as well, there are many good people ready to help newcomers to rays.
If you are able to find one, buy a tank bred ray from someone in the US who has bred the animal him/herself.
Get ready to do large frequent water changes and feed a lot of live food such as nightcrawlers and blackworms.
Rays are hungry critters that demand pristine water conditions .