I struggle w this too.
Sometimes it is hard because you think...
"am I being unreasonable or too harsh because
I think this isn't OK ???"
We are so accustomed to people pleasing that we question when it is time to protect ourselves. If you have to question it, there is a very good chance it time to set up some boundaries.
The bottom line is, there are some shady people out there who
will try and get away with treating us poorly, unfairly or various other things for their own personal reasons.
Often people test out our boundaries when they know that are doing something they shouldn't but want to get away with it.
There is nothing wrong with saying, No...that's not OK. It can be difficult but it is one of the most self loving things you can do.
True, it takes some practice and isn't always easy. But, you should try and
do it knowing that you and your piece of mind are well worth it.
If you struggle try and again and don't give up.
You deserve to be treated well and have solid boundaries.