Deals that are too good to be true are often not true. $4k is very cheap. Either this is a scam, the horn has problems, or someone doesn't know what they are doing.
I own 3 Borgani Jubilee horns (straight soprano, alto and tenor). I love all three, BUT both
the alto and tenor had manufacturing problems that caused their original owners to sell them. With the tenor, I'm the third owner. Since I don't play in public, I had
the luxury of fiddling with the alto and tenor each for a year or two, taking them over and over again to a good shop as I find more issues, until they finally play like they should.
In one sense, I got great deals -- I have three horns (two of which were about half retail) that I play and have no desire to look further, but it has taken several years to get to this point. if I'd had to play the alto in public, I would have had a problem -- it was just very hard to play The kind of problems I had on my Borganis include: leaking necks (both alto and tenor), a hole in the octave mechanism that was oversized, preventing a positive seal of the body octave on low notes, bent cups, poorly installed (not enough glue) or cheap pads, loose rods, bent tone cups, plus the usual slightly uneven tone holes. So you ought to play this horn to see what you are getting into. Once a Borg plays right, though, you will love it.