Hmmm, things to look for with a A3000...
1. battery problems. I have 2 a3000d's now (as of last week), both had leaking batteries - one was leaking badly but it seems it started recently.
2. ZIP memory. It's expensive and afaik there are some cases where some fast memory on the motherboard is needed, even when memory on an accelerator or zoram is present.
3. buster. my 3000's rev.9.x came with a Buster7, the 7.3 with a -09.
4. ROM version. If it comes with 3.1 roms all the better... motherboards with a ROM tower are harder to replace (I could not get the tower out).
5. floppy faceplate. If only one floppy is installed, does it come with the plastic faceplace in front of the second? the A3000 comes with the floppy openings by default - one of which can be shielded by the frontplate.
6. int21 modification. If it's done this means the SCSI on a accelerator card can be used.
Jus what I could think of!