I currently work at a Jiffy Lube, and I can tell you that it is not the company that's the problem. Just like any other large chain-company, there are always bad examples to be found. At the Jiffy Lube I work at, we have two guys that have worked in the company for 25 years between them, and another couple who have worked there for at least a year each. I'm currently half-way through mechanic school, and take my job seriously a training in the field for a career working in an actual full-service shop.
We work hard, and provide every service we charger for, without exception, admitting defeat and taking items off the bill that it turns out we can't service (i.e. Jeep fues filters, as mentioned).
I'm not saying that all Jiffy Lubes are like ours, and I'm sure they're not...I even know of others in our area that aren't. I think just like any other shop or garage, it's caveat emptor, or, let the customer beware...you've got to find a shop you can trust, and check their work even so. There are still honest workers out there, in every company,
~Erik~