Retics are small, but they are not the smallest. Since their tail length is so much longer compared to other rays, with respect to their disc size, they actually need a fairly large permanent housing situation. Scobina rays are the smallest, but prepare to dole out a hefty fee for one. I'm pretty sure due to shipping restrictions on their country of origin that they aren't readily available.
NOW if you DO want retics, which I wouldn't advise against, I would make sure you're getting them from a reputable dealer. I could go into countless stories about parasites and finicky eating habits, but they're as depressing for me to type as they would be for you to read. If you do get retics, get live blackworms!!!
First let me start off by saying thanks for the response. What rays would you recommend to a beginner?