If one is not mechanically talented -

Make sure it works before you buy it.

Which can also be a challenge for a newbie that has no idea of how a machine is supposed to work.

some " surprises" ive had (because i did not know sny better)

There are left homing machines - I did not know that
a motherboard that is kaput will be renamed and not replaceable
Really old machines have spindle bobbins or use uncommon needles

I think i would rather buy a machine that Grandma used a lot and nay have worn spots than a machine that was hardly ever used.

Again - if possible, make sure it works before taking it home.

If an instruction manual is still available - Bonanza!!

Just ask Mr. Google ...
... he has many manuals at the ready for you!
No matter the age of the machine.

Bear, I have a machine I was told works. It does - if 'works' means it gets power and the needle goes up and down. But it doesn't sew!

it's like a used car; you have to take it for a test drive!

I bought an older Bernina at an estate sale. I had owned one so had a bobbin and casing to take with me. I also took needles, thread and fabric to make sure it sewed well. A lot of sellers just turn it one and press the foot pedal and say it works. As Cathy said, not always so. If I'm paying more than a few bucks for it, I want to make sure it works.

I have bought a couple machines at garage sales for $20 without testing, but they were old Singers that appeared to be in good shape. One I mostly bought for the case which would fit my 501 that I didn't have a case for. It's a 401 and I still haven't tried it to see if it does sew. I also bought a 185J in a table that I really bought because it was only $20 and was so cute and little and GREEN