I would recommend against getting one at all.
They are Very likely to fail and are Not easy to repair.
Only someone who has attended several LaserDisc service seminars
(which, of course, have not been held for many years and won't ever be again)
should Ever even take the cover off a unit, let alone go poking around in it.
Special test discs that were never cheap and may be hard to find are needed,
as are several pieces of highly reliable test equipment.
Setting up to do such work today would cost a lot.
Few repair shops are going to put money into Anything
that won't make them much, if any, profit in return.
If you Simply Must have one, get nothing older than the Pioneer CLD-D703 and CLD-D503.
Models newer than those would probably be even more preferable.
(I Own a CLD-D702, which is a Little Less wonderful
in terms of performance and reliability than the '703.)
You should know that DVDs provide better performance
and Much Less Trouble at a Much lower cost than LDs.
LDs are Very heavy and take up about as much space as four DVDs.
Except for some music and specialty titles,
they have two sides to be played, as with an LP,
which makes for an unavoidable interruption in the flow of a film.
Some longer titles have to be divided onto three or even four disc sides.
When I first bought into LD in 1993,
things were very different from the way they are now.
These days, I would Not put a Single Cent into LDs.