It doesn't take too much pre planning before hitting up an auto parts store to be smarter than the counter parts person.
When needing a belt or simple electrical part for the tractors, mowers, willys jeep, etc......I'll tell them what I'm looking for or give them a part # to cross reference to anything they have in stock. When asked, "Whats this for?"......I tell them an experimental science project and anything in stock that crosses to that part # given will work.
One time I needed a new cheap 12 vdc starter solenoid for the '48 Willys Jeep. At the parts store I was asked what's it for? Me: Doesn't matter....its a science project. Parts guy: We don't sell parts for science projects. Me: You don't stock simple 12vdc starter solenoids? Parts guy: Yes, but I need to know what its for. Me: Show me what you have in stock on your computer and I'll show you what I need. There, that one is perfect!
Within a few minutes I was holding a $10 starter solenoid and was heading out the door. It seems if the part's counter person is under 50 years old.....they don't have a clue how to think out of the box and find something that can replace what you're looking for. LOL!!