AgentZero said:
"Just for fun, I decided to take an IQ test (www.tickle.com) and scored 156. Rather impressive, you may think, however I took a different IQ test from the same website a couple months ago and scored 182."
Search your local library for a tiny book written decades ago called -- "How to lie with statistics". It addresses this problem specifically.
Short answer, you won't get exactly the same answer with each measurement, and 25 IQ points is not a significant difference.
If the website wanted to be responsibile, they'd highlight that by providing % error information. Like political polls do.