Well, I think you should buy mine :-). See
www.337skymaster.com/p337.htm.
Other than that, I suggest you be careful to buy a 337 that has been well maintained. Because of the low initial purchase price, 337s attract more than their share of twin owners that find the maintenance costs of a twin higher than they expect. (And that is ANY twin, not just a 337. Because of more difficult access, maintenance costs on a 337 are perhaps 10% higher than a Seneca for example, but the benefits of the type to a pilot are VERY much worth this tiny extra cost.) Buying a 337 that is "down on its luck" can make your wallet down on *its* luck for the first couple of years....
I suggest you search to old messages in the forum, as well as those on
www.skymaster.org.uk. You'll find lots of answers to this question....
Kevin
webmaster@337skymaster.com