2007 (Touring Edition) alignment issue . . . or not

Took my car into the local chain tire shop 10 days ago for rotation. They noticed excess tire wear on front and rear, outside 1/2" or so and recommended an alignment check, so I got one and cleared them in advance to the alignment. (Since I rotate every 5000 miles, it's probable that the front wear happened while those were rear tires due to the misalignment explained below).

At pickup, the said that they had been able to do the alignment, but would not be able to adjust my wheels in the future unless I had a shim put into my rear right wheel. They explained that they had been able to get the rear wheel within safe bounds.

Original Camber on the right rear: -1.3; post-alignment: -1.5
Original toe on the right rear: .31, after: .17

I called my local Toyota specialty mechanic and he admitted he didn't know much about that so he referred me to a specialty alignment shop. Called that gentleman, and he explained that shims cannot be used on my generation Prius; if it is out of alignment and can't be further adjusted, work needs to be done on the axle, but he needs to look at the car first because the measurements from the chain tire store are probably inaccurate. On top of it all, the specialty shop claims that my camber readings indicate a need for axle work as well.

This thread indicates that shims are a real option. But it also suggests that shimming is not necessary unless the car is out of alignment (which it apparently isn't).

I WILL NOT take my car to the local Toyota for service (long story).

The local chain shop says they will shim both rear wheels for $170 parts and labor included, but that it doesn't need to be done now. What confuses me is how they were able to get it into alignment; if I understood the thread from the link above, they shouldn't have been able to. And I am a little leery about a chain shop doing more than oil change/rotation/alignment on my Prius.

Nor do I want to take it to the specialty shop if they guy there doesn't even know that shims are an option.

Nor am I quite sure whether I need to get this done ASAP or just eventually, before my next alignment, say. I do need new tires soon, and have a day off today and can make calls and even take the car in somewhere.

I drive a lot, 20,000+ miles/year, so poorly wearing tires would be a big problem.

I have very little mechanical aptitude and tend to depend on trust. Right now, I don't trust either option and my trusted mechanic doesn't deal with alignments and his referral hasn't panned out.

My question is: what should I do next and how soon?Any suggestions/observations/answers appreciated.

 

Thanks for the responses! I am in Santa Barbara County, CA. A local recommendation would be wonderful.

Barring that, if anyone has a recommendation on what to ask prospective alignment specialists when I "cold call" them in order to winnow out the charlatans, that would be helpful. I would assume alignment specialty shops do calibrate -- asking if they do insurance work might guarantee that.

Should I ask something leading, like "I need a rear alignment for my Prius" and see if they know enough to start talking knowledgeably about shims?