I don't collect cards anymore, but nowdays it seems that the graded and cards numbered with a "serial number" are more in demand and get better recognition as legit. I don't know of the cost to so this, but it may be worthwhile on the more valuable items. They are graded and placed in protective sheaths. The grading is pretty much widely recognized by collectors as a standard.
I had my complete sets (1980's & 90's) of cards stolen from my mother's house recently. Unopened full sets with rookie cards of the likes or McGuire, Sosa, Ricky Henderson, etc. Plus my Johnny Bench rookie card, but they left the 65 Yaz... Fools. Up in (crack) smoke they went...
eBay will get the most money in many cases, prey on the emotional bidder... The one that *has* to have it...
Offer up the good stuff just in time for Xmas...