Are GRE Practice Guides Easier Than the Actual Test?
Assuming you are referring to the GRE General test: It would depend on what materials you are referring to, but the popular ones, particularly those from ETS, closely match the difficulty level of the actual test. However, note that:


To get a more accurate impression of difficulty, try to mimic test conditions as closely as possible (e.g., practice online tests if you are giving the computer-delivered test). Even if the questions seem easy, time could be an important factor, and familiarity with the interface helps. ETS offers two free online practice tests that use the actual test user interface.
The difficulty level is adaptive based on the section. So, if you perform well in one section, you can expect more difficult questions in the next, and vice-versa. However, the scoring is weighted based on section level difficulty, so ideally this should not adversely affect the final score.