Treat them as any other salons, there are awesome dominican stylist and awful ones, same as in everywhere.
Do a consultation first, and go for another thing like a rollerset or a treatment and watch how she does other client's relaxers. I would ask if you can bring your own relaxer (personally I don't like to switch relaxers and always bring my own,and now I'm a DIY) and if you can bring your own protectant for your relaxed ends (I use Mizani Honey Shield), how long does she process the hair for, and what outcome you want (bone straight, some texture to it, etc)