Everyone is entitled to their opinions, but I think so many people have misconceptions about used items is general. These people usually think linearly in that, if it's used, it has problems. Let's be realistic here.
First off, I don't remember the release of the 99-04 body style, but I'm assuming late 1998? I purchased late 2000, so that's more like 2 years old.
Anyways, a used car having mechanical problems as the reason being sold early on is probably one of the least likely reasons. Think about it. You buy your $27k 2005 Mustang GT and love it to death. Twenty thousand miles down the road, being completely under warranty, it has a mechanical problem. Would you screw the warranty and quickly sell it back for $13k as fast as possible? If you liked the car, that would be completely ignorant.
What are some likely reasons the car was turned in after two years?
1. A Mustang GT was not right for them--it didn't offer the comfort or performance they desired.
2. The person was in financial trouble, bought the car new, and simply couldn't afford it. Rather than struggling through life with no money, they had to sell the car.
3. This person was not satisifed with the snowy traction, and it simply wasn't a practical car to own for their yearly driving conditions.
4. They bought a silver Mustang, and in 2000, they really wished they had purchased black, and the new headlights and scoops were the deal breaker. Furthermore, they decided it was time to upgrade to Cobra or another special model.
5. The lease was up, and it was time for something fresh. Many people like to upgrade cars every 2 or 3 years.
6. Manual transmission was fun at first, but it really was a pain when they lived in a city with traffic, or they did alot of traveling.
7. The person/people were trying to make this a family/friend car, when no one could fit in the back.
8. They needed an SUV to haul stuff. It just was an impractical decision and an impulse purchase.
I could go on and on, but I won't bore you all. The fact of the matter is that mechanical problems are not the likely problem. If they liked the car and it had mechanical problems, it would be fixed under warranty. And looking down the road after warranty was up, how many people put $14k+ into a car soon after?
Purchasing a car slightly used is a bad decision? Yeah, let's buy a Mustang after it has no warranty, and the sold reason being mechanical problems is more likely. I had 16k miles left on warranty when purchased. If I felt the car was not confident in reliability, I could turn around and sell it a year later if desired.
I have this exact same trouble convincing people that buying used items off Ebay aren't flawed. Ahhh...some people will never learn.