Has anyone found a good way to listen to speakers on the used market before buying them?

I think you're overthinking this.  If you buy for a good price in the used market from a reputable seller, you can likely resell the speakers for little or no loss if they don't work out for you.  That's precisely the beauty of the used market.  Yes, it takes a little effort to box up and send the speakers to a new owner if necessary, but in the scheme of things the used market, used wisely, is an extremely cheap way to audition speakers in your own home and in your own system.  

It is difficult to audition used equipment especially speakers, let alone discontinued models. One reason why there are so many for sale - people buy unheard and then have to sell. Selling speakers can be a pain, depends on what you sell, the price, your feedback etc.

When you figure this one out let us all know.

Realistically, for pre-owned, out of production speakers, the best you can do these days is to find reviews of the speakers and try to make sense of what the reviewer thought they heard, given their system context, and then make a decision based on that. Probably not what you were hoping to hear, but it can help narrow down the choices somewhat. Even at the peak of the brick and mortar heyday of the late 90s, there were still severe logistical problems. I am still feeling "burned" by a Vandersteen dealer in San Francisco when I listened to badly implemented demo in the shop while evaluating a pair of 3A Signatures. Whatever preamp and amp they were using had the volume all the way up, and yet the speakers weren’t even cracking the 70 dB SPL. So when I ponied up with a credit card requesting they let me home demo that same floor pair, the owner refused, citing prior damage experience. So I called and spoke to Richard Vandersteen, who was nice and helpful but simply shrugged and told me that, "yeah, some dealers are like that." And this dealership was the ONLY Vandersteen dealer in the entire Bay Area. No wonder (&^^$@#^%&^! excuse the French) brick and mortars are going down rapidly. Sorry, I have to vent this experience for the hundredth time. I ended up with a pair of Dynaudios from a competing dealer that did let me home demo them before purchase. Ultimately, I too became part of the Thiel family where I have remained since.

Speaker selection in this day and age is very risky. There is simply no way to know without listening, and there are few listening opportunities. These days you have to pretty much begin by "listening" with your eyes and try to translate that into a quasi-visio-sonic experience, in silence. Not good.

And then there are great, intelligent companies like PS Audio, Schiit and SVS that let you home audition for a period of time before permanently keeping the purchased product. More need to adopt this practice; it’s the only way they will ever succeed in this day and age. If I were in the market again, I would gladly check out the SVS Ultra towers.

+1 to soix

I bought used Lyngdorf 2170 without auditioning intending to sell it if I do not like it.

But it turned out to be keeper.