Not sure I would be trashing a shop so hard, If I couldn't install a gas tank myself..... sounds like they did exactly what you ask them to do, and you ask for something that was gonna cause a problem....
You haven't seen the other threads...and I haven't thrown names out on the internet. "Sure I can install a TTI exhaust. Just a few hundred in labor...That'll be $5,000". And I wish that was the only invoice line item.