Check their warranty. Don't want to buy a $600 paperweight or spend that much again on a repair.
Yeah that could be a problem with the Zeiss. Germans ain't got the best reputation for warranty service even if the product is covered.
This is what spooks me on a used scope.
You should be good with the better US scopes. Most of them are lifetime transferable warranty. One exception to that is Redfield. Their new owner, Leupold, won't honor the warranty on older scopes.