Yes, unfortunately, test prep which provides familiarity with the types and formats of questions does not yield the most ACCURATE test result, although it may, in some cases, yield the HIGHEST test result.

After taking any particular IQ assessment, there is a required waiting period before that test may be taken again. Using a test prep which replicates the puzzles, challenges, and/or patterns of the scheduled IQ test is an unethical means of circumventing the interval requirement.

Acceptable IQ test prep and IQ test administration is covered in several old posts and discussion threads. Here is a brief roundup:
1) http://giftedissues.davidsongifted...._much_error_can_there_be.html#Post199479

2) Hoagies List of psychologists familiar with the gifted - https://www.hoagiesgifted.org/psychologists.htm

3) Test prep articles: one by Aimee Yermish, one by Nadia Webb - http://giftedissues.davidsongifted....t_do_you_tell_your_DC_be.html#Post174222

4) Full Scale IQ (FSIQ) vs General Ability Index (GAI)

BTW, here is a round up of older posts on many frequently discussed topics on this forum: http://giftedissues.davidsongifted....ps_of_links_on_frequent_.html#Post236361