Paying $10 for something you don't feel is worth that price means you'll be dissatisfied with having paid it. I'd have walked out without paying that price for that very reason.
Otoh, that means I'd have had to go find the part elsewhere and maybe ended up back at the same shop later if I couldn't find it cheaper - definitely no happier, but I'd have left with the part then.
It's the gamble you take any time you buy something retail --- different shops, different inventory and prices.

I'd mark this shop/experience in my memory and probably not return there for small parts ever again.