I agree that used is a crap shoot, but I will add that out of 25 + ukes (I have lost count) I have bought, all but five were bought used without playing first. The one that came with the twisted neck was made by an overpriced IMO Island builder, was well used and damaged in that usage, and offered on eBay by a very high end specialist Hawaiian reseller who shockingly to me did not disclose the visible damage and thus I would not buy from him again. The cheap used Kala that came smelling of pipe tobacco and smoke finally aired out. A few others were not to my exact taste but they were ukes I wanted to try. I figure it was worth the few dollars I didn't get back from resale to "rent" and enjoy them, and I paid on average half to two thirds retail, which let me get a higher end uke than if I bought retail. Usually I got a case as well and did not have to pay tax, just shipping.
If I wasn't willing to try buying used, I would not have my pre-fire Maui Music six string, and I do not see ever being able to afford a new Peter Lieberman build. It needed a minor setup which I did, it has busage and it is awesome. I waited over two years for an MM I could afford, and I had tried to buy and missed several during that time. I buy my cars used too, I have never owned a new car. I let other people pay full price, and I get a cream puff a few years down the road at half or 1/3 the retail. Our newest car was $40K new, we got it with 60K miles 7 years later for $6K. I get $80-$100 shirts (I love Territory Ahead) for $6 at Goodwill. I guess it is mostly a mindset.
If one doesn't have the ability to check out and setup a uke then new with a setup is the way to go. Play it for awhile, sell it for another if you aren't well satisfied. I have had more issues with Kamakas than any other brand, and I'd say play those in person. I bought one used in person, one used online that had an issue but which was due to age and correctable. They show up on local Craigslist out here in Los Angeles periodically.
I would also vote for Pono as excellent build quality and sound, I had one previously that was circa 2005, the quality has come way up since then. I would also be interested in the KoAlanas made by KoAloha in Thailand that will be available soon. They will be mahogany. My mahogany Pono six string is awesome. I don't think you could go wrong with any of the Ponos.