Grade and/or condition does not need to be discussed at all when making an offer for these or any other coins. Discussing grade and/or condition does nothing but put the buyer and seller in two different opposing camps.
If you only talk money, then you won't set up quite so insurmountable a barrier between you. You do need to be confident in the offer you make and you do need to have a good idea of grade NOT based on sellers opinion. If you need to be "safe" in your offer, that's the best thing and will give the seller an honest opinion of what you believe the coins are worth to YOU.
I've bought many collections from collectors, collector's heirs, hoarders, silver stackers, and about any other "category" you can think of that would have coins to sell.
The one thing I can absolutely guarantee is that the more complicated you make it, the more problems that can evolve. Doing a deal based on a supposed
TPG guarantee, or another dealers opinion, or any of the other possible options (with the exception of pictures posted HERE) only allows for more problems to develop.
Make an offer. If it's good it's good, if it isn't, you know.