My first several months of getting back into the hobby, I had no strategy for what cards to buy. Nevermind which cards to sell or hold - I could only think of acquiring cards. And I know most of you out there are the exact same.  That's great! That's why they call it "The Hobby." You should be buying cards. But I think it's important to have a strategy as to which ones you're buying and why.  Using data from Starstock (I have no partnership with them - they definitely have no idea who I am as of this publishing date), I have been able to start to determine which players, which cards, and which grades of cards (including from which grading companies) I should buy, try to sell, or hold if I already own.  Using two players that I'm extremely high on right now, Angels P/DH Shohei Ohtani and Knicks PG RJ Barrett - I break down data from Starstock.  I love that Starstock shows you how many total cards they have in their vault, and how many of them are listed for sale. In general, the sports card strategy principle is - the lower the percentage of a player's cards for sale, the more valuable the collectors see the player's cards being long term.  Breaking that down further, on a per card basis, you can look at say Shohei Ohtani's 2018 Topps Chrome Rookie vs. his 2018 Topps Update Rookie and contrast the percentages. It may be that all Ohtani cards are mostly being held; or it may be that only a certain number of them are.  With Panini cards for example, you can do your own comparison of Prizm vs. Hoops (or another set).  Then, another one I'm fascinated by, is by grade and grading company.  So on the Ohtani comparison in this video, I find that his PSA cards are being held, but his SGC cards are being listed for sale. So PSA is still seen by collectors as the more valuable as a long term hold based on this data.  The Barrett data comparison supports the same conclusion, as the PSAs are being held, while the BGS graded Barretts are being listed.  I hope this content helps you in crafting your own data-based sports card strategy.  I'd love your thoughts in the comments.  Happy Collecting!