It's a good idea to ask to inspect a nuc before committing to pay. Typically you would go mid to late afternoon and look at the brood and brood pattern which would likely give an indication of overall health of the colony. This would also give you an idea of the temperament of the bees which you could also factor in to your decision. You then wait until evening, seal it up and toddle off.
Varroa can be indicated by more than just seeing mites on a drop- another method to consider is to open a couple of drone cells and remove the pupae with tweezers to see if you find any varroa.
An honest question - the way you type and address some on here does not come across well. Are you aware?