I am planning to attend a PhD program in the future. Should I be honest that I have some experience of attending a full-time Master degree in the past for three years? I had a somewhat rocky relationship with the thesis supervisor resulting in me being kicked out from the program. I am a bit worried that revealing this might be not too beneficial for me during the application process. Can I pretend that I did something else during the three years? In reality, I did some work in a part-time manner while attending my old program (self-employed).
Consider the worst case scenario under each action: telling them and not telling them.
Under the first it might be a bit harder to get accepted and your search might take longer. You have more to explain about how you will be a success.
Under the second, you are found out and expelled and blacklisted for dishonesty. Academia is a kind of a small place in each discipline.
The best scenario for both is about the same.
If nobody asks you, of course, do not mention your Master's program. However if you are asked (or if you have to fill out a form about your previous education), you must absolutely not be dishonest!! If for some reason they found out, you could be executed (is this the right word?) from.the program immediately. When asked why you did leave the other program, be diplomatically. Do not badmouth your previous supervisor. Say something like "it wasn't a good fit".
Moreover, did you really think in a forum full of academics like this one (some registered under their name!) somebody would really encourage you to commit fraud?!