What to ask when buying used speakers?

Will do.

I'm happy for the folks that can spend 2.5x the used price to avoid the risk of used gear.  I, on the other hand, have only been able to have a taste of high end audio by buying used.  

Yeah, I've gotten lemon gear. But overall through the life of the hobby there's no question I have saved over 50% of the new budget by buying mostly used gear.

I agree with the advice above that the best protection is getting to know the seller.  For any significant purchase, I invest my time in ongoing dialog with the seller. Not only does that "make friends" and make the transaction more pleasant, but you can get a very good sense of the person, their knowledge and treatment of gear, and ultimately build trust with them.  

I also buy a lot of used gear from Andy at Saturday Audio in Chicago.  He stands behind everything and the gear is thoroughly checked out.  He's swapped out speakers for me when something was amiss.  This is the type of dealer relationship you will also want if you are building an ever-evolving system. 

One thing I would say is that buying some components from a smoker household may not matter, speakers are big and right in the room and pick up (and release in your house) the smell of smoke worse than most other components.  I remember having to wash some ML panels in my shower to make my room livable. 

Used gear, and navigating and negotiating...that's part of the fun for me! I have met a lot of really nice people, all walks of life, all layers of society. You'd be surprised what gear some guys who make $40K per year actually have! 

@bigtwin if only others would ship items like that. Wow. Most NEW speakers don't arrive in such good packaging. Wish they would. 

@mtbiker29 cats can shred grilles. Friend of mine made chicken wire cages around his ESS speakers back in the 1970s because of that.  He spray painted them black so they didn't look all that bad with a stained hexagonal wooden base at the bottom.  Even worse are dogs that can piss on the speakers and leave a very bad lingering smell. Same with humans who smoke tobacco.  I bought a used laptop computer once that stunk of cigarette smoke for months.  I'll not make that same mistake again. 

For ported speakers, watch out for any bugs and spiders that might be lurking inside. Even new speakers can host such creatures. 

@grislybutter laid out a number of the well-known precautionary steps, all of which I agree with.

I’ve purchased 4 or 5 pairs of 2-way monitors/speakers and had very good luck. I followed those precautionary steps, plus one other that needs to be discussed: protected transactions. And that usually means either Paypal’s "Goods and Services" category of transactions; or using a credit card; or both.

I really dislike Paypal. It’s a parasitic organization that siphons off ~3% of each transaction, more than some credit cards. They also burn you down on currency transactions, which if/when you buy from another country (in my case, Canada); in such cases they make exchanging currency unavoidable and offer rates considerably worse (ie, more profitable to them) than any bank. .

Another factor must be mentioned regarding Paypal: there is an avalanche of ignorance out there about the IRS’ planned (not yet implemented) program to tax some (not all) of Paypal’s "G&S" transactions. The net result of this is a LOT of sellers proudly demanding Paypal payments only via "Friends & Family," which is an unprotected transaction with huge risk.

But I digress. When I buy speakers, I insist on using Paypal’s "Goods & Services" feature. If that’s not acceptable to the seller, I walk. I also save all Q&A in my transaction w/that seller as a pdf file so I can prove (if necessary) that, for example, they said the drivers were intact and functional, yet they arrived non-intact and non-functional.

Finally, I’m not a fan of face to face transactions--going to someone’s home, or them coming to mine. It feels risky to me. But the only time I made an exception for that was one time buying a pair of vintage speakers (mid-’80s vintage KEF 103.2s). I needed to see and hear them in the seller’s system.