I get where you are coming from - kind of - but basically if your intent is to return the suit after you wear it I think you are in the moral wrong. The things are expensive. If everyone did what you plan on doing the prices would be even worse. A good shop can talk you through what is best for your size and skill level.
I bought a CAT5 TYR from trisport. It was clearly used so I guess you aren’t the only one who has thought of doing that.
I really don’t understand the “immorality” of trying a wetsuit in the water (I think suits should be designed to withstand moisture damage). Of course, if the pool water causes a problem (e.g. I don’t rinse it out) or I used it for a month or I rip it when putting it on, then I accept the responsibility of buying the suit. I have never noticed any damage to a suit after swimming in it once or twice. This is not much different than taking a bike out for a test ride before buying it; it could be argued that bike testing is worse as there is a reasonable chance of road wear on the tires. Asking a shop to just recommend a size/model is like asking the Ford dealer which car is best for me (they are unlikely to try to sell me a Mazda). Find me a shop that sells all brands & sizes and I will check them out. TriSports has a pretty good selection and even they don’t have half the models I am considering (19 Rogue, Matuse, Aquasphere Racer, Xterra Vendetta, Huub). Local shops have crap selection at best even if I were willing to drive 50+ miles and spend a day or 2 shopping. I live not far from Philadelphia so I can imagine people living far from a major metro area would have even worse selection.