Part frozen rats what should I do

[Bogertophis]

If they were still ice-cold enough to be partly frozen, I would think they're not likely to be spoiled, & be OK to re-freeze promptly & feed as needed.

If, however, your snake tells you otherwise (be refusing to eat them), you might defer to their expertise on the subject, as I personally have never eaten a rat, lol, spoiled or otherwise. (Seriously, snakes have a very keen nose & most will refuse spoiled rodents.)

The proper temperature of a refrigerator for our use is 40*, & food certainly can spoil at 40* or even less. Basically a freezer should stay about 0* but at that, bacteria is not killed, it just cannot multiply. In between 0* to 40* is a gray zone, so the colder the rats stayed & the longer they stayed that cold, the better (safer). As you said, if it was your food you might not worry so much- and one main difference is that your food is cooked & that kills most (if rare) or all the bacteria (if well done). The other difference is that our food is just "meat", not the whole animal with guts & all that's FULL of bacteria just waiting for a bit more warmth to proliferate. You're right to be concerned.

I'd let the seller know, as this should not have happened, they should have been packed well enough to remain frozen...that's a reasonable expectation on your part.