The credit-only sites
DOPA converts an unwanted card to credits at 100% of its listed value. Credits buy DOPA packs, nothing else.
Packs.com buys cards back for Coins at the estimated resale value shown at reveal, and PackRipper reports Coins can't be cashed out.
Drip Shop Live's blog puts its Instant Pack sell-back at 88% of market value, paid as credit. Its terms say promotional credit has no cash value.
Why it matters
A credit sell-back keeps the money on the platform, and the easiest thing to do with it is rip again. That's the main reason we rate DOPA and Packs.com Caution.
None of this makes the sites illegitimate. Just know before your first rip that any money you get back has to be spent there.
How to get value out
Request shipping and sell the card through a marketplace, after checking recent sold prices for the same card and grade. Count shipping costs and the time it takes, since Packs.com estimates 2 to 4 weeks.