Only if that is the stores rules. Who wants to buy a melon that you've groped on? But if the rule says grope first buy later than it is OK. Kinda like corn. Don't peel back the husks and check it out. That isn't the right way to check out an ear of corn. Who wants that ear of corn?All dried out and tough. Nope, the rule rules!
Besides, if you are good enough in the kitchen you can do amazing things and never be disappointed. That disappointed thing is very overated.