- There is liability. If the bike falls apart the pro whose hands it went through might be seen as an expert who would know the difference between a safe frame and a dangerous one. It doesn't mater whether that is true, just so long as it sounds reasonable enough to get named in a suit. The liability is believed to be real enough, because there are a growing number of parts suppliers who don't sell to non-pros, without a track record, and insurance. Not even having the basic tools would sound like a lower test still.

- There could be a risk to the tools or the bike, and the shop isn't covered if the newbie maker did something that would add to wear or time to deal with gooey residual acid flux. If something happens to the tool, who is going to cover the several hundred dollar cost to the shop. What about if the shop can't get a good cut because of all the distortion from a newbie. Is it the kind of thing you can delegate to the guy who changes tires, or is the shop owner going to have to get involved, when he is already busy.

- The home maker is really a competitor to the shop. He either doesn't think the shop sells the right stuff, or he wants to compete with him down the road. It is like the guy who goes to Wal-Mart for his stuff, but brings it for service to a local shop.

- The bike business really doesn't like amateur builders. I can think of lots of other activities were non-pros are doing crazy stuff and nobody blinks an eye. When I used to rock climb, I would buy these "parts" from a store, then go and rig a cliff with protection, from what I learned from a book. I started at 12. Never had a problem. Seems way more risky to me than brazing, but to hear the Pollyanna's talk it is all going to end badly. Same kind of attitude that faces any new development like a carbon frame. Or the attitude to show bikes. Totally conventional thinkers.