What Happens When They Don't Grade?

If they aren't already slabbed MS-70 by one of the reputable TPG then ebay's Buyer's Protection doesn't apply.
A grade is an opinion and the ones that are considered most acceptable by the market are NGC and PCGS.

Opinions about raw coins are strictly "you vs. me".
If you think differently than the seller, that should have been settled immediately.

If you try a crossover of a slabbed coin and it downgrades, that's even worse.
It has nothing to do with the seller.
And the original grader won't give back the original grade.
It might not be the original coin or at least it's been handled again by someone else.

Bottom Line: It's up to you to agree with the original grade, particularly when dealing with raw coins.
And if you want to do a return of a raw coin that is difficult because you've handled it.

Don't know how that works, it's a presale though and in the listing they are naming the grading company and offering the MS70 grade, so I'd think it's misrepresentation if they deliver anything less than what they advertised in the listing

However they have:
"AS THIS IS A PRESALE LISTING THERE IS A
NO CANCELLATIONS
NO RETURNS
NO REFUNDS
Policy"
on a lot of the listings.

Still though, misrepresentation is misrepresentation, and fraud is fraud, so I'd think they would either need to deliver a MS70 from the grading company indicated, or issue a full refund for the item unless you thought delivery of something else was a reasonable resolution.

What makes you think 60-80% or more of these coins won't be MS70 by the way? They should be, that's what all these folks are banking on happening.

Giving A PCGS, or an ANACS, or A O instead of a CC as indicated, or even giving a 1921 D instead of the 2021 D lets say, isn't going to work no matter how many disclaimers they have on it.

However, I have no idea how ebay or Paypal handle it. Shouldn't be an issue if you get what they represented you would.

I looked up and found "you can request a return regardless of the sellers settings on returns if it is delivered not as described 30 calendar days after the estimated or actual delivery date or within the seller's stated returns window, whichever is longer"

30 days from the date you received it, or whatever other that is longer.

it has to be "not as described" though.