One excellent resource when shopping for a used model is the Kelley Blue Book. Unusually, I find the interface at cars.com to the KBB info to be easier/quicker to use than the actual kbb website. The Kelley Blue book values are based on auto auction sales values across the country.
Let’s look at the 2008 Cadillac STS-V. Blue Book® Values for a 2008 Cadillac STS -V Sedan 4D with 24,000 miles in ZIP Code 75023 on 08/09/2010: $34,695 from a private party, up to $39,695 at retail. A dealer would offer $31,325 for a ‘trade-in’ value. This last figure is not directly useful, but it does help to establish a range. If one could find a prime example for sale from an individual they are hoping to get $31K-34K from the sale. A Dealer is hoping to get from $39K to infinity.
The National Auto Dealer’s Association distributes the NADA or ‘blue and orange’ / ‘yellow book’ pricing. The NADA guides would suggest a clean trade-in value of $36K, and a dealer clean retail value of $43K. Average trade-in is $34K.
A third source dealerships sometimes use is the ‘Black Book’ car guide from blackbookusa.com, which is updated weekly and is focused on wholesale values. Although this information is not available online, check with your Credit Union as they frequently also carry valuing guides. Black book online access is $397/year for daily updates or $298/year for weekly updates.
A research-based method of course is to utilize online searches and monitor the prices asked for the model you have an interest in. In this case the three lowest 2008 STS-Vs with under 24K miles on cars.com are at $38.7, $38.9, and $39K retail, and more or less hovering at that price point for the last few months.
Of course an additional price point to keep in mind is what the automobile is worth to you. The fact that Ferrari sells cars for $whatever amount does not make their offering worth that to me. In this case although the STS-V sold new for $79K+, the low $30s is the amount it makes sense for me to purchase a very clean, excellent used example. So until I can find the ‘right’ deal a bit lower than the current asking prices I need to keep shopping.
And REMEMBER when shopping — you are not in ‘love’ with any of them. Maintaining your objectivity is the MOST important way to find the right car.