Definitely buying. When I buy, I try to ask myself where will this card be in 5 years and will I be happy with this purchase at that time. Of course there’s no way to know for sure but after decades of collecting and watching prices of various collectibles (baseball cards, comic books, MtG, etc) that’s where I’ve settled out. I don’t buy cards to invest per se but I don’t want to lose money or waste money in the long run. Some version of the mantra that smpratte coined here “older minter better” is what I have always followed.
Some other rules I follow… I don’t use money that I will need. I treat money spent on collectibles as “gone” even though it’s not. I assume if I immediately resell any card I will lose money on transaction costs like fees and shipping at a minimum. I will let myself take profit/get liquidity on things I’m not emotionally attached to, things that I upgrade or that become extras, or things that weren’t part of my original goals.
I also try to treat my collectibles as a portfolio. If it turns out I overpaid for something or the value declines I will let it go at a loss if I have other gains to off-set. Case in point, I bought a complete 1st ed base binder set for $8k a few months back. It ended up being an extra, and I just sold it at a loss of roughly $1k to a forum member. At the same time I sold a 1st ed jungle booster box I bought for $4.5k a few months back for $6750. I’m fine letting the two wash out and churning the capital into something else I care about, which in this case happened to be a 1st ed base set PSA 10 lugia.
Probably TMI but some may find that thinking helpful. Collecting that way can help you be calmer and less worried in a time when prices seem to be racing ahead. A lot of people seem to be worried about the rising prices, but to some extent you have to expect that will happen over the long term. Will they keep rising next month, or 6 months from now? I don’t know but I largely don’t factor that into my decision making.