How reliable are the soil test kits found in gardening stores?

Here are the advantage of the garden store soil testing kits:

They are cheap (provided you use your kit more than once or twice).
They can give you a very general indication of your soil pH and fertility status if that is all you want.

The advantages of sending a soil sample to a professional laboratory are:

The results are much more accurate. You will know your soil pH value within a tenth of a pH unit and your nutrient results will accurate within a few parts per million.
Your soil sample will be handled by a professional staff of technicians who run these types of samples every workday.
If you only need a couple soil samples tested a year, the cost of the kit will not be a real savings (especially since chemicals age and need to be replaced).
You will receive recommendations specific for whatever type plant you want to grow. The recommendations are based on the latest university research data base.
If you need further assistance, an Extension county agent can give you follow-up advice. If you use a kit, it will be very difficult for the agent to help with interpretation since the kits use different extractants and sufficiency ratings.

There are more accurate kits available through such companies as Hach and LaMotte but now we're talking hundreds of dollars.