there's tons of good advice here, but here's my two cents worth.
If the maker is around see if they support the model that interests you. Some stop support at five years out of production... some further. BW Nautilus went out 10 years after production... other BW models went only 5.
Check to see.
If the company isnn't around let's hope the drivers & xover parts still are and you're handy with a soldering iron and so forth.
If neither of the above are in force.... I'm pretty sure I'll pass on the whole deal.
My Phase tech two ways are 30 this year, but were 100% refitted two years ago at the Phase Tech plant. they were a gift in the first place... but I called the maker to see about the aspect of support, anyhow. two weeks of playing and one speaker died.