As a seller, speakers are by far the worst item to sell. When we say things like fully tested and performs flawlessly, I can tell you at least what I mean. I connect them to my system and put them through their paces. I listen to tracks and check if I hear static or distortion. If everything checks out....it is fine. These are speakers. They are not that complex to test. Incidentally, I do the same thing when I test gear. Need to test all inputs and outputs and make sure everything works. DACs and servers are most annoying things to test.
That said, speakers are hardest item to ship. I have had two issues in 5 years which is higher than on any other product type. In one case, FedEx beat the hell out of the box and the base of the speaker was damage. This was $150 item that was easily removed and replaced. The other, FedEx beat the hell out of the box and a glued piece of wood came loose inside and knocked a wire loose on the crossover. In that case, it was an inexpensive repair. Both cases, I covered it. Clarify what happens with your seller if something goes wrong.
Other notes. I would want to see them in original packaging and depending on the type of speaker, might insist that it ships freight rather than UPS/FedEx. I would flex on this if you were buying from a very reputable seller that has purchased packaging materials from someone like ULine or has it professionally packaged by FedEx. Then if anything happens you have a checkmate on the people at FedEx and they have to pay the claim.