Use guest checkout whenever possible. If you do need to sign up, give fake info, or highly redacted info. If I decide later they actually need it, I can update it in the account settings. Nobody's ever cancelled my account because I said I was born Jan 1 over 120 years ago. Do digital purchases via some middleman, like a PayPal account backed by a credit card, Apple Pay, etc. Lots of sites have PayPal checkout flows…
This way I can be reasonably sure they've tied all my activity to my singular account. Instead of my shipping address, IP etc being all over the place. When they don't have a delete account button, I request it via email. Seems to work fine. Obviously can't be sure it's actually gone, but that's okay. Ever since Adobe leaked my PII, it's out there anyway.