Bent brake drums after installing new rims

[angrygenerator]

A couple of days ago, after noticing a noise from my front wheels when driving at highway speed, I took to my local tire shop. After running diagnostics they determined that I needed a new rim, and that I needed to have them replaced immediately or risk an accident. They wanted $650 for the repairs, but being a little wary of tire shop mechanics I figured to I would get a second opinion at a a auto repair shop who I had dealt with in the past with good results.

The second shop after doing some diagnostics ($90) said that that my car had in fact two bent rims and would repair everything for $350 plus tax. This quote didn't include a tire alignment like the first shop, and they would used rims ($95 dollars each) instead of new ones ($150 each). We figured that since the tires seemed to be wearing evenly, an alignment probably wasn't necessary.

I went with the second shop, because I felt they seemed more trustworthy. On Friday I picked up my car and everything seemed fine. On Saturday morning, my wife was on the highway and suddenly without warning, found that our Yaris began to shake up and down rather violently every time she touched the brakes, and later even had trouble getting it to make left turns.

We had it towed back to the shop on Saturday and this morning I got a call from a mechanic at the shop telling me that my cars brake drums were bent.
He didn't think it was his fault for not noticing this and now wants another $150 plus tax to replaced two of the break drums on my car.

Is he correct about it not being his fault, or could something have happened when installing the replacement rims to cause the drums to become warped?

Also is there a market for bent rims?