I have bought literally hundreds of instruments online, over the past 25 years or so.
The number that I would not have bought in person? Perhaps half a dozen, if that. And that is largely due to build quality issues with the specific copy that I got, not due to making mistakes regarding what I like and what I don't like.
Let's see if I can name them:
1. 2013 Gibson EB with significant build quality issues (screwed up body contouring/sanding). Guitar Center, on sale as B stock for under $700 delivered. The pickguard also didn't follow the pickups very well, resulting in some unsightly white poking through. And, I thought the Babicz bridge was a mediocrely made unit. Sent it back for refund. I would have bought this model in person, but not this copy. Also, I now regret sending it back, as they prove to be rare and expensive in white, and I could have stripped it, filled the problem areas with Bondo, and refinished it with a better looking gloss white finish, instead of matte – and installed a Hipshot A style bridge. I would like one some day, but not for the $1,000 to $1,200 people are asking for them. They were $1,000 retail price when new, and ought to be $750 at most on the used market, IMO.
2. Recent D'Angelico DC 90. Musician's Friend. Sold it for more than I bought it for on sale, and bought another for the same sale price. The second copy I received is the model of perfection, outshining most import guitars I have ever played. Again, I would have bought this model in person, but not the first copy that I received.
3. Hofner Club Bass from Pro Audio Star. Strings were garbage, tuners were garbage, and fretboard was not perfectly straight. Nut was poorly made. I would not have bought this model if I had played it in person first. But I had got a very good deal on it ($465 brand new,
with its proper Hofner hard case), and it does have a certain special something that none of my other basses have. So I rectified these issues myself, rather than sending it back.
4. G&L L-2000 1983/1989 Frankenbass. Guitar Center used buy. Showed up with warped neck and being a parts bass, not to mention that during shipping, it busted through the top of the Roadrunner hard case that I had purchased for it to be shipped in. Found out, thanks to TalkBass, that the bass had been sold and returned at least two times prior, for the same price. I reamed them about it in an e-mail, and ended up getting the bass for about $600 (sans case). I straightened the neck myself. Definitely would not have bought this in person, because I would have asked to have seen the date stamps in the store first.
5. Epiphone Elitist white Les Paul Custom, from Music 123. Purchased brand new, circa 2003. Showed up with diagonal finish cracks under nut (headstock probably took a whack during shipping). Sent it back for a full refund, and never replaced it. I would have bought the white Elitist LP in person, if it hadn't been screwed up like that. In the end, I got the Elitist SG instead, which got stolen. I replaced it with an open book headstock (Japanese domestic market) version of the same thing, for half the price. Sold it to my bandmate, and he still owns it (I gifted him a set of Seyour Duncan "unofficial Jimmy Page" pickups for it, and installed them, and it rips).
6. 1982 G&L SB-1. Reverb. Bought it relatively cheaply (about $470 after tax and shipping) knowing it had some issues, like having been poorly refinished, and having had the original electronics replaced. But it showed up with a wildly warped neck, a thick, gummy overcoat of clear on the neck, and a painted over bridge – all of which I had specifically inquired about with the seller prior to buying, and been assured that these things were not the case. I tore him a new one for lying to me, and he claimed stupidity, not malice, and offered (and sent) me $325 back, so I ended up getting the bass for $145. I would not have bought this bass in person for $470, but I would have for $145, just as a parts bass (which is exactly what it has been used for).
7. G&L L-5000, here on TalkBass. Arrived with serious issues that the buyer had misrepresented, even when specifically asked about them prior to purchase. Buyer claimed stupidity rather than malice (which I most definitely did not buy), and offered a 40 percent refund – which only sort of satisfied me, because the whole situation left a terrible taste in my mouth. Similarly to the SB-1 above, I would have bought it in person for the amount I ended up getting it for in the end, but not for what I initially paid for it – and I could have done without the attempted screw-over by a member of this community.
8. Music Man Sterling Stingray Short scale in white. Pro Audio Star, brand new (not B stock), but negotiated down 25 percent to $450. Showed up with a huge fretboard ding on the treble side edge. I asked to send it back. They offered $60 back, to get it repaired. I took the repair money, and then steamed the ding out a bit myself, then filled the rest with brush-on polyurethane. I then stripped the neck, dyed it a classy yellow with alcohol-band aniline dye, refinished it in clear lacquer, and put a beautiful gold and black pre-EB style Music Man decal on it. Then, I special ordered a real Music Man U.S.A. hard case for it. I definitely would have bought this model in person, but not this copy.
So, I guess it is over a half dozen...but I can't think of any more at the moment. Not a bad miss rate for 25 years of buying online.
Notice some commonalities among these? Four out of seven of them are from gigantic chain stores (all of which are now conglomerated; Music 123 was not owned by Guitar Center at the time of my Epi purchase). The other two of the eight that were not from a private party were from a cheesy blowout retailer that doesn't post anything buy stock photos (Pro Audio Star). No problems whatsoever from
Sweetwater, Chicago Music Exchange, Wildwood, Wilcutt, Dave's, or other better run, classier joints.