How to prove brake tabs need to be faced?
 

I know that they need to be and I got my disc brakes working but I want to run something that aren't avids. The manufacturer of my bike (bikes direct) want proof but it's hard to see on camera. I went to a bike should a couple of months ago about it but they said they could just adjust it so it doesnt rub, but I want to get the most out of them (tektro miras)

"I know that they need to be"

I know that I want to get out of dealing with cycling customers. So, you got them to work, the LBS says they can adjust them to work, BD doesn't see the problem, What exactly are you trying to convince me of?... "It's calendar time for Buddy"...

It's not that they don't see it, They want a photo but the caliper is not very misaligned so I'm not sure if they will see it. I wanted to know if there was any other way to show it better, other than from behind the bike. I would like them faced to get the most braking performance out of them since they are already weak.

If they can be adjusted to work, getting them "faced" (I'm assuming you feel they are somewhat out of alignment in some way) will not improve braking, it might make them less prone to rub if a problem does indeed exist with the bosses as you "know".

So, why not just get them faced and be done with it? Are you looking for some kind of price adjustment, or what is your goal?
The reason shops invest in frame prep tools is because they often do not come perfectly prepped from the factory.
I've done countless bottom bracket shells, head tubes, and yes, brake tabs that were not perfectly done at the factory. They cut corners so they can sell you a cheaper bike. Most of the time, they're good enough, but can always be made better.

I was hoping to get it done and compensated by BD since it came from the factory like that. How much would I bike shop typically charge for that?

Dude, you got a really cheap bike from an online seller. One of the things you give up for that low price is this kind of service. You’re about as likely to get a price adjustment from them as you are to get blood from a rock. Take it to a shop and pay them if you really think that your brake tabs need to be faced. But they probably don’t need to be faced.

Next time, if you want this kind of after-sale service, buy your bike from an actual shop.

You are asking for a level of quality not normally included with bikes, and certainly not with budget-oriented online sales of bikes. If it's that important to you, get it done yourself. But I suspect the fact that the brakes can be made to work acceptably according to the professionals you showed it to, but not to your more rigorous standards of perfect alignment, is only a problem in your eyes. Either pay for the alignment out of your own pocket, or take it up with your therapist.

I'd agree that at that price point and with BD's business model the appropriate expectation is that the brakes can be made to not rub with reasonable lever throw. One thing to check is if there is uneven paint build up around the brake mounts--you can scrape this off with a razor blade and fix a lot of misalignment. As for cost, it's hard to say. Disc mount facing tools are fairly expensive and low volume shops may not use them often, and some of their staff may not know how to. Actual time is probably about 15 minutes a caliper for just the facing, but they may upcharge beyond sheer time, plus whatever their normal rate is for a mechanical disc brake adjustment. If you have incredibly steady eyes and hands you can improve alignment making small adjustments with a flat file--assuming you don't remove too much material, the worst is you just need to bring it in for a proper facing with a tool.

I expect to face all disc mounts. Is is just something you do if you build a bike well, like chasing threads. The factory might have done it, but I wouldn’t assume so. Certainly not some kind of defect the manufacturer should address.

Assuming the problem is what you describe, between $60 and $120. Most likely though, the misalignment, if it exists lies somewhere in the brake itself and/or the mount or adapter. Would have to actually see it to diagnose. Like someone mentioned above, BD frames are, lets say "basic" and it may be an issue of tolerance, or even paint on the mounting surface.

How do know they need to be faced? Kind of hard to tell you how to convince them when we don’t even know why YOU think they need it.