Don't forget the possible tax advantage. Here in MA, sales tax is 5%, and you pay it on the difference between your trade and your new car. So if the SRT was $80k, and you get $50k, you are paying tax on $30k ($1,500) instead of on $80k ($4,000). So if someone comes along and offers you $52k on the car, you would be better trading it in, because you get $500 more, and you are not liable for any potential lemonade law.
(note, I don't mean lemon law, I mean lemonade/lemon-aid law. This is a private/consumers version of the lemon law. In MA it states, I belive, that if a car needs repairs to pass a safety/sticker inspection, and if the costs to exceed those repairs are more than 10% of the purchase price, the buyer can return the vehicle to the seller)