Will be visiting a wheel shop shortly to check up on practice etc.
Nothing official and calling it an audit would be a rather gross overstatement but I still will need to check up on things and how well it's run.

Problem is, it's not exactly my degree of expertise (Part of the visit is to learn about their operation).

Anyone with suggestions into what's best to:
a) look into and check
b) what to check for
c) how to check it
d) and other miscellaneous ideas.

Thanks.

I would look for the obvious easy stuff first. Is it well kept? If the shop is a mess how well are they going to treat your product? Do they follow safety and environmental rules, including their own. Some of that falls under the general housekeeping. It also shows if they follow directions or just those they feel like. Talk to the lower level people in the shop if you can. Ask them to show you how they access technical manuals or safety info to do their job. Look at how they store and use calibrated tools like torque wrenches and measuring devices. Everything should have a calibration date and be neatly stored. That would be my short list of the 'Low Hanging Fruit'.

Thanks.
Do we have any more in depth ideas?

How is nonconforming product handled? Is it segregated from production? Do they have written processes for rework/repair?

Greetings from someone who audits wheel shops!
A few pointers:
Calibrated tool currency. Allow me to repeat what someone else has already said, for emphasis. Torque wrenches, etc need stickers or documentation proving that they are both calibrated AND that the calibration is not expired. That's usually pretty quick- most places put stickers on the tool.
A valid quality control program, and a reasonable level of oversight.
Easy access to manufacturer's manuals, approved publications, or whatever it is that they're supposed to be doing their work in accordance with.
My company also demands to see a drug testing program.
In a wheel shop, I also want to see how they're tracking MY parts and keeping them segregated from other carriers'. How do I know that my wheel halves are being isolated properly, so that someone else's bearing doesn't get put into my wheel!
NDT testing, if applicable. Any training on that? Any certification to perform?
If you're going to do a thorough job (for an actual audit), you need to put your Quality Control hat on, and be a bit demanding. There's probably a better way to say that; don't be a jerk, but don't be a pushover, either. Be PROFESSIONAL. Your company spends good money on wheel work- it's in everyone's best interest to make sure that things are being handled properly!
The facility you are reviewing shouldn't be able to tell whether you like them or dislike them- that's bias.
I can be a bit of a booger, even if it's people that I'd willingly go have a beer with at the end of the day!
But that's okay- it's a responsibility not to be taken lightly.
The most important thing I learned in auditor school (yes, that's a thing, but it only took two days! More of a seminar) was that you DON'T have to be an expert. You just need to be able to verify that a standard is being used, and adhered to. So first, know or find the standards, and second, have them show you how they're complying with that.

Cheers, and best of luck!

Training/certifications. How many A&P license-holders. Supervisor to line ratio. Recordskeeping. Records backups. Access to data archives. Complaints file. Volume of work on your particular parts. What's the repair station's FAR Part 145 record?