Hi - I've been using my mum's 60's Singer Starlet sewing machine since I was a small child and somewhere along the way it became mine. I recently treated myself to a new one - the Janome 525s - and have already made a full-sized teepee and some dragonfly wings with it 
The old Singer needs to be sold as I just don't have the room but I'm not quite sure what to do with it. In recent years, the tension became a bit of a problem and really I should've got it seen to/serviced but just struggled on with it. It does stitch, but the stitches don't look quite right!
It seems to be a bit of a collector's item and the one I have has got all the original bits (case, manual, pedal, lead etc) but it would have to be sold as needing attention I think.
So really what I'm asking is, is it likely that someone would pay a reasonable amount for a sewing machine that needs a bit of attention, or is it worth me investigating the problem and fixing it first? I'm a bit worried that it would cost more to investigate than it would to sell!
If it would help to see photos of the stitches I can post something later...