OK, time for my 2 cents here...
I too am a dealer. Not much experience...less than two years. Prior life was Navy Officer. 16 years active, and still a reservist. I don't sell Vipers or any other exotic. My inventory, which averages in number anywhere from 35 - 50 vehicles, has an average age of nine years. I sell mainly cash-only. Less than 10% of sales I finance in-house. Monthly sales in recent months have averaged 24 vehicles (yep, I use "average" a lot!).
My bread-and-butter vehicles are Ford F-150s, Dodge D-150s, Chevy C-10s, Blazers, Ramchargers, Broncos, Camaros, Spirits, Cavaliers, 5.0 Mustangs, Monte Carlo SS', and some older (mainly Mopar) muscle cars. The occasional Neon, Probe, Intrepid, Lincoln, or even Range Rover sneaks in there.
I recently sold a 1992 Chevy S-10 ext cab 4x4 (70K miles) for the fourth time in nine months. Why? The first buyer is a friend of mine and decided he needed something bigger. He initially wanted that truck because he thought it would be better on gas than a full-size truck.
The second buyer wanted a new $30,000 truck on a $4000 budget. After he complained that it rode too rough and occasionally made a "popping" sound in the front suspension once a week or so, he decided that he made an error and needed a newer truck. I then traded him into a low-mileage 97 F-150.
The third buyer wanted a small 4x4 to use during hunting season. After hunting season, he decided he wanted a cheap SUV to get ready for beach season. He traded it in on an 87 K5 Blazer.
The fourth buyer bought the truck a month ago, ripped out the 4,3 V-6 and dropped in a ZZ3 350 crate engine, stronger tranny, etc, lifted the hell out of it, put on big 38 inch tires, and is currently enjoying the 3rd or 4th level of redneck heaven.
People are fickle. Needs and desires change. In all cases, the buyers returned to me because I treat my buyers like they are the most important people in the world to me. They are in a way...they pay my bills and allow me to provide for my family and buy Vipers and Mopars for myself!
I very much want the S-10 back when the current owner tires of it. I can sell the hell out of lifted trucks in my 'hood ;-)
(BTW I love my job. Not just being my own boss, but being around vehicles all the time is a motorhead's dream!)