If you get a shop to build wheels for you, how accurate would you expect them to get the dish on the rear wheel.

I just had a set built up and the dish is very slightly off (about 1mm) toward the drive side. Not a major problem, it just means adjusting the brakes when I swap to my other wheels.

How hard is it for a builder to alter the dish and would you bother?

I would say this is ok but certainly it can be fixed just needs to get it closer. My question is what did you use to measure the dish being off 1mm. If you can measure that accurate on the dish ( not that hard to do) then that says you have pretty good skills. The builder should be able to alter the dish in a heartbeat.

I just put it in my frame and the rim is closer to one chain stay than the other, 1mm maybe 2. Very easy to see. I have 2 other sets of wheels that sit perfectly central in both my frames. It was seated correctly in the drop outs so I concluded the dish is marginally off.

My frame is fairly tight for clearance so im worried that under certain conditions the reduced clearance could become a problem

I don't consider a wheel build done unless the dish is off by a lot less than a mm.

The dish should not be off at all. There are basic shop tools for this.

Obviously their truing stand is out of adjustment (it happens). I would let them know (and ask them to finish building your wheel).

Personally I never use a truing stand for dishing, they're not accurate. That's what dishing tooks are for.

This. My first set I built both wheels were out of dish because the truing stand I had was out of adjustment. Getting it back in adjustment was a pain in the arse, should have tested the stand when I got it (used) on an existing set before diving into the build.

doesn't sound good to me; take wheels back to the builder and ask them to verify the wheels being true round and lateral, and same dish on both sides, and tensioning (shouldn't be any the ring too high or low compared to other spokes on the same side)

if they start turning nipples, are they putting tape on the spokes to detect wind-up? more of a concern with the thinner double butted spokes like Sapim Laser

you should watch the verification; if they are true, have them put the wheels on the bike and have them check the side to side offset you notice

wheels that are "finished" and not dished evenly on both sides are a pain in the ass to fix and there is risk that the tensioning will be incorrect; if I had a finished wheel that was not dished correctly by 1 mm I'd loosen all the nipples and start over

I might be showing my lack of ability/knowledge, but I don't worry about dish being 1mm off.

1mm is within spec.

I think i'll mention it to them but I'll measure it first so I have numbers to back me up. Im guessing 1mm but i suspect it is more given that I noticed it the moment I put the wheel in the frame. If they dont want to know, its not the end of the world but its my first hand built set of wheels and Id like it right.

That was my thought as well. There's no way a 1mm difference would be so obvious.