I've run into plenty of players in person and read about their signing habits online where they enjoy adding to their own collection or will reward fans with cards they've received from other collectors. For instance I was at an in person autograph signing for a player who played in the MLB for several seasons for some popular clubs but he wasn't necessarily a superstar. He came to the signing prepared to sign anything for those who came but also had a stack of easily 150 of his cards from various teams and sets. I'm fairly certain the duplicates collectors sent him to sign he ended up signing and giving out to fans who came unprepared to meet him. Personally I have no issue with that and hope my extra Topps card can be a memory as the first piece of a collection for a kid who met his first big leaguer and walked out with not just a stadium giveaway hat signed but a nice clean autograph on a vintage Topps card.
Some of my best TTM autographs are Whitey Ford, Craig Kimbrel and Billy Wagner.