The only dress that I’ve had TOTALLY ruined was at a wedding. Part of my degree was in textiles and if anyone can get a stain out, I can. Someone bumped into me, I didn’t notice it and they spilled champagne. It was a fabric that could go into a home washer and dryer. I dried it and heat sets any stain (that’s how they set dye). I didn’t notice it until I took it out of the dryer.
I’m going to a formal wedding this summer as well. My dress is beautiful and it was under $100. I’ve already worn it once and machine washed it. I now air dry everything like that.
Another thing to consider. How would you like to buy new clothes that had been worn and returned like you are suggesting?
IF the store does, by chance take it back, they can’t re-sell it. They take it as a loss. Losses are made up by higher prices (as are shoplifting costs). Basically what you are suggesting is theft that others may have to pay for.