I've learned to walk away...and have many times.
I've probably bought several pins that most people would walk away from. The only pins I buy are ones that have potential. Sure....I'll sink 120+ hours into the restore...but that's the funnest part of the hobby.
I've only truly regretted maybe 2 or 3 purchases, but those particular pins didn't stay long in my collection. The problem I have, sometimes, is I "feel sorry" for a poor neglected pin, and "going over-board" on the shop job.
But that's what I like...bringing old neglected pins back to life.