Hi Sharleen,
Thank you for participating in our forum. It's new and we hope to get a lot of good information posted shortly.

This is a good question and I will tell you my opinion as a long time resident married to a Costa Rican girl.
CarsIn my opinion you should buy a car in Costa Rica rather than importing it yourself. I have made calculations based on cars that are not popular in the US and are popular here, hoping to make a profit on the lower value there and the premium here, and it doesn't work out. By the time you pay shipping, insurance, customs broker and the actual tax, you are very close to market value here. This is especially true for later models, since a lot of people have gotten into the importation business and the margins are very slim.
If you buy the car here you can test drive it, you don't have to worry about shipping damage and you don't have to bother with customs. If you buy new car and ship it here, you won't get any warranty from the dealer.
Domestic AppliancesI am also in favor of buying common appliances here, because you will have a warranty issues. Another factor is the repair possibility. Manufacturers market different models in different markets, so even if you stick to a well known brand you may not find the appropriate parts here.
ExceptionsThe only exceptions in my opinion is in the case that you are shipping down things that you already own. If you have a car that is good for Costa Rica and you purchased it new or know that it is a good car, then I would say it is worthwhile to ship it down. The same with appliances. Even though they eliminated the exemption officially, I believe you can also get a break on the import duty for things that are obviously shipped as household items or personal, used goods.
Another time when you might wish to buy overseas and ship here is if it is a specialty appliance. Sewing machines are a good example, a lot of Ticas sew, but I am pretty sure that the fancier machines don't sell well here, so they would probably be prohibitively expensive. Another example are portable items like digital cameras or video cameras. I had my parents bring down a DV camera last year when the visited, the same camera is not even available here and the DV cameras were hideously expensive. The models I see advertised are probably 2 years behind the model I have and about 75% of the price I paid. I would have gotten an even better deal if I had been able to wait for a good sale or liquidation.
I hope that helps and don't hesitate to ask for more detail!