It's a tough question! I try to only take in machines that are in decent condition and look like they will restore well but I am also really attracted to a challenge. I'm ok with dirt, grime, funk but not ok with lots of rust and corrosion. I can re-wire, re-hab motors, and love troubleshooting a machine that won't work. For me, I have to believe that once I have it stitching that someone will want it. If I can't offer it life working again sewing for someone then it's not worth it for me.
I love finding deals though and sometimes a seller wants to get rid of more than one at a time. I still have machines from my first bulk buy and several of those are not in the same shape I would shop for today but it was a bulk deal and many of the other machines were salvageable.
I just picked up three machines last weekend for 20.00. I really only wanted the 15-91 but when they were still unsold at the end of the weekend, they made me an offer I couldn't resist. The 15 and the 27 are both machines I can save. The Fashionmate wasn't worth the effort. I do not hurry to save a machine with plastic and this one had tons of rust in the bobbin area and was missing parts as well. I stripped it for parts and am ok with discarding it.