How to check quality when buying reprap prints from people?

This is a tough question for all of us. I have printed printers for a few people now but when I started I was very nervous that my quality might not be up to scratch. I kept tweaking the printer and printed parts for my own printer, then finally decided it was time to sell something.

I posted an ad on the reprap forums and got an order for parts for a printrbot without extruder from a guy in Portugal. When the parts arrived he sent me this message:

'Hi 

The parts arrived this morning, some could use a bit more infill and smaller layers to make them stronger. Some holes are small, others are too big, looks like you need to tweak your printrbot a little more. 

Besides that, they look good 

Best regards '
Ok - so he didn't ask for a refund, but I was certainly dissapointed - at the time his parts were some of the best that I'd printed and I only had online pics to compare my prints to. I thought they were great, but he was obviously not impressed. I had printed him structural parts for a printrbot with only 10% infill and .35 layer height. Since his message I have recalibrated with a proper set of calipers and I always print structural parts with 30% infill. I also reduced layer height to 0.2 apart from some models where the STL is optimised for 0.25 layer heights. Since then I have also never had a complaint, not only that - but I've had a lot of compliments from clients about the great quality of my prints.

Soon after this I broke a pulley and didn't have any spares. I asked a guy on ebay to print me 4 of them as I'd broken that particular pulley a few times and the quality of his prints was far superior to my earliest sales. After buying a glass plate and slowing down my prints I can now safely say that my prints are good enough that no one will complain again (I hope!).

Back to the point of this post - when you buy reprap printed parts from someone online you have to think beyond the normal set of scams where that happen all over the place. You can do basic check like asking for a photo of them next to their printer and making sure they didnt take it from google, but quality wise they might not know they have poor quality prints, or they might just be stingy and printing very hollow parts with low infill % to save on cost of plastics as well as thick layer heights that speed up prints but increase the chance of delamination.

I think it's best to ask for a set of photos showing their printer and some closeups on some printed parts as well as asking what layer height they print in and what infill they use. For printed toys you may get away with low infill but structural printer parts that a lot of stress and need a high infill %.

What's you're experience been the quality of the parts you buy?