Did he actually show you what was wrong with it though? A lot of guys at pawn shops like to talk big about stuff they barely know. I thought my first paste job was bad but it turned out I just used way too much and it squished out the sides, which is messy but not gonna kill anything. The real crimes are not cleaning the old stuff off first or forgetting to plug the fan back in. So unless he pointed out something specific, he might have just been messing with you.