There are always two sides to a story.

Charging a total of $400 to r&r a rear lower control arm including an alignment, shop supplies and tax is very reasonable. In this case the customer self diagnosed the issue and supplied the parts. So the shop lost out on parts profit and had to deal with a 30 year old car to boot.

It's a thirty year old car, is it reasonable to expect that by replacing a bent suspension part with a good used one and nothing else is going to eliminate all the wandering issues? On a high mileage old car like this, the front AND rear suspension likely has multiple issues causing the wandering. Not to mention, the condition of the tires is suspect due to abnormal wear cause by worn and damaged suspension parts.

The shop demanded payment first because that's the way business is done, asking for a test drive before making payment is unfair to the shop and is a real slippery slope.

If the op had taken the car to the shop with a specific complaint of wandering and pulling to one side and they then performed the full list of recommended repairs then there would be legitimate gripe. Something caused the control arm to bend, probably an impact with a curb. Likely there is other damage that the op isn't able to diagnose himself.

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"I was a dirty bird, Carol's not grungey - she's *****in" John Milner....American Graffiti