I bought a set of Testors flat acrylics from Hobby Lobby as experimental/practice paint. I only use Tamiya for AB'ing on models. I thinned Testors w/ IPA and it sprayed very well. However, unlike Tamiya acrylics, Testors almost look satin. Is this how they are supposed to look?

Never have tried testor's acrylics but try their thinner first and see how the results come out . Sometimes the thinners have an effect you don't expect . I tried brushing Lifecolor paints thinned with water and it gave me the tide water marks , switched to their brand of thinner and it works .

Any variation from the manufacturer recommended materials can give unexpected and unwanted results. Also, there are certain issues of age when buying a paint product from a retailer who might not move a lot of that particular item. hobby Lobby, love em as I do for certain things, isn't really highly dedicated to plastic models or supplies and from my experience, the items sit on the shelves for a very long time in certain cases and just deteriorate from age. I have experienced this buying Testors model paints from several Hobby Lobby stores in the US. Paints do not have an unlimited shelf life.
Before you give up on the paint, get some fresh from a real model shop and use the correct thinner.