Feeling disempowered/sexism at work - handling it

I've worked at my company for 3 years and in that time I'd say ive been on the receiving end of 3 sexist clients. I've worked in the industry for thirteen years.

The first example became so nasty we fired him - at the time my boss commented he wouldn't have behaved that with a male employee.

The second time was when I had explained the value of making a specific choice and my recommendation wasn't taken. A month later a male colleague delivered the exact same advice & they listened intently telling him what a wonderful idea it was.

Last one happened today and I feel bad about it. I gave a recommendation based on recent results. The client told me that if my boss (male) said the same as me/supported what I had said, he would take it on board and take the action. I have felt terrible about this all day - I feel like I've been doused with cold water I feel so disempowered. This person also made an inappropriate comment early on and calls me nicknames which to me suggests he doesn't see me as an equal.

I also have some great clients, both men and women, who treat me with respect and take my recommendations and would never say 'let's see what your boss says.' In this scenario I of course said I would consult the boss if that was what they wanted - but I just felt like screaming why is my word not good enough?

I used to be self employed and scenarios like today remind me why.