im having issues with new marketplace listings - help me on what kind of accounts to buy

If you're logging into purchased accounts from the same device or IP, they'll get linked. You'd make sure the accounts actually have Marketplace access. Some don't, so check that first.

Also use a clean residential proxy. if your account is US-based, you should use a US ip and match the timezone.

Isolate each account with an antidetect browser, one unique fingerprint per account. And don't log into multiple accounts from the same browser.

I'd be careful about assuming account age or friend count is the solution. Marketplace reach can depend on listing quality, location, category, pricing, competition, and account trust signals.

Since purchased accounts can also have an unknown history, I'd first test the same listing variables on a legitimate account you control and check whether the issue follows the listing or the account.

I will go with older accounts with like 5+ years and have some friends before using marketplace to look more legit

It's not necessary to buy long-standing accounts; instead, buy accounts that already have a spending history.

Account age alone may not be the main factor behind Marketplace reach things like account activity location, seller history and listing quality can matter too.
Would be interesting to see whether established Marketplace activity makes the biggest difference.