One would think that reliable applied to a soil test would mean that the information from a retest of the same sample would give the same results. Nope. "reliable" means that you can rely on the fact that the test is being performed according to widely accepted methodology by qualified people. You'll never test the same sample twice and get exactly the same numbers. There is always going to be variability even within a small sample, regardless of methods and reagents. (If you ever did run the same test twice on a sample and get exactly the same numbers, something went wrong)

Your University of Illinois Cooperative Extension Service no longer provides soil testing, although they do have a list of labs that will. Get a good soil test done. That "soil specialist" at that nursery is suspect because of his statement that the fertilizer you were using was not working properly and he had another one that would, without looking at the plants or doing a soil test. You need a good reliable soil test to determine what, if anything, needs to be done. These simple soil tests may also help. 1) Soil test for organic matter. From that soil sample put enough of the rest to make a 4 inch level in a clear 1 quart jar, with a tight fitting lid. Fill that jar with water and replace the lid, tightly. Shake the jar vigorously and then let it stand for 24 hours. Your soil will settle out according to soil particle size and weight. For example, a good loam will have about 1-3/4 inch (about 45%) of sand on the bottom. about 1 inch (about 25%) of silt next, about 1 inch (25%) of clay above that, and about 1/4 inch (about 5%) of organic matter on the top. 2) Drainage. Dig a hole 1 foot square and 1 foot deep and fill that with water. After that water drains away refill the hole with more water and time how long it takes that to drain away. Anything less than 2 hours and your soil drainsâ too quickly and needs more organic matter to slow that drainage down. Anything over 6 hours and the soil drains too slowly and needs lots of organic matter to speed it up. 3) Tilth. Take a handful of your slightly damp soil and squeeze it tightly. When the pressure is released the soil should hold together in that clump, but when poked with a finger that clump should fall apart. 4) Smell. What does your soil smell like? A pleasant, rich earthy odor? Putrid, offensive, repugnant odor? The more organic matter in your soil the more active the soil bacteria will be and the nicer your soil will smell. 5) Life. How many earthworms per shovel full were there? 5 or more indicates a pretty healthy soil. Fewer than 5, according to the Natural Resources Conservation Service, indicates a soil that is not healthy. Here is a link that might be useful: UI CES

Many labs do test for nitrogen compounds, and there are multiple classes of tests: ammonia nitrogen, nitrates, several different nitrites... The N test in this kit apparently isn't testing for ammonia nitrogen, because it does not indicate high N for household ammonia. Without participation in a 3rd party conformity assessment program, there is no assurance that laboratory test results are reliable. If you doubt the reliability of home test kits, you should also doubt the reliability of laboratory test kits.

There aren't any reliable soil tests for N. Just so you know. Anyway, check out these professional quality kits from Lamotte. I've used the Turf Lab Field kit and found it useful. The other professional kits are detailed under the Agricultural section (model AST, STH in particular). One thing about these kits is that you have to be serious about taking tests. The chemical reagents do not have an indefinite shelf life. Here is a link that might be useful: Professional quality test kits