I was looking at some All mountain 1's last night on ebay, I was tempted to bid, but kept reading about faults with them due to quality issues.

How bad are they to buy second hand? Any top bomber buying tips?

Avoid 2008 and some 2009 forks
Avoid the air forks with the dodgy travel adjustable air cartridges (ATA TST?)
Go for coil sprung Z1's or something like that from around 2005 – 2007 and you shouldnt go far wrong.

avoid TST2, some years it is very unreliable and even when working it is a poor damper, similar to the 'turnkey' damper RockShox use on their most basic forks.

Are they for owning?

i ve got some all mountain 1 s with lock out no travel adjust they are a little heavy but very plush and smooth, hold air pressure well, ride great had them on bike for 18months now and good as new. were old new stock when i bought them not sure on year.

Given there's not that much variation in price with old Bombers, I'd hold out for something with top of line damping.

What that was called seems to have varied a lot from year to year 😀

There's also a guide to upgrading one of those Bombers (I think the AM) to shim stack damping, which would give a fancy damping setup at a low price.