I've tried this many times on the message boards, and it just gets buried under the For Sale threads. Might be quite a good idea. I'd look through there if I knew I might have a 10 cent card that somebody will pay $10 for.
My message boards posts have netted me ZERO cards. I posted one video on my YouTube channel and another collector got me a lead on a card I needed to finish a set. He got $20 after I completed the transaction. Targeted/specialized works.
2012 2013 2014 2015 2016 be the year Panini finds Marvin Harrison & Marcus Allen to sign their NFL's Greatest Signatures cards?