Because they vary a lot, and the "collector value", they can either be very very good deals, a horrible waste of money, or anywhere in between. For THIS thread, all generalizations are pretty much pointless. Judge the bass you have the opportunity to buy entirely on ITS own merits to YOU and nothing else. You have the chance to play it personally? If so, that means you can determine for yourself whether it's a good choice for YOU.
Don't listen to anyone pontificating about how bad they are, or how awesome they are (and I inject a lot of "they ain't as good as they should be for that money" when we're talking about that era in general). You're not buying a general example, you're buying a specific instrument. Therefore all the blather about sloppy neck pockets, so-so fret work, clumsy feeling necks, unique and wonderful tone, shoulder-breaking weight, iconic appearance, etc. are meaningless. Just play THIS chunk of wood and metal and decide if it works for YOU.
Now if the questions start to center on whether it's authentic, then post some detailed pictures and there are a lot of folks on TB who can help with the minutia of that frankly confusing era. But if you're sure it's what the buyer claims it to be, and you like that particular bass (and not just like the image of having a late '70s) then it's a good deal for YOU.
John