I'm not "worried" about it, I just keep a strict budget. Making allowances here and there is a slippery slope, plus this gives me the oportunity to be a hardass in negotiations.
I've come up with a plan B: Quid Pro Quo. Basically, you buy my car at an agreed price, and I buy yours at an agreed price. Instead of giving me trade-in value toward cost, they give me trade-in value as a check, which pays off the old loan. Then, I lock in the adjusted purchas price at 6.4%.
I like the Jag, but I'll have it checked out by a professional first. They've also got an Audi A4 1.8t worth looking at, but I'm more worried about its reliability then the Jags.