2. Advice (which is essentially a gift of knowledge/experience) is not something you are entitled to by virtue of your sex.
3. A man cannot be said to be 'sexist' when he chooses not to give advice that could potentially incriminate him, especially falsely. If a person (whether a man or a woman) chooses to keep silent, and especially where no fraudulent aspect is involved, that is part and parcel of doing business. You are not entitled to call a person 'sexist' just because they do not want to give advice to you.
4. There are virtually no consequences to the woman who accuses. Yet in comparison, the long-lasting consequences of an investor being falsely accused in public far outweigh any advantages to the contrary. This is enough to make any man clam up, and is a legitimate cause to withhold advice.
5. More importantly, in a commercial setting, no one is obliged to give you an advantage just because you're a woman. If you expect such an advantage/benefit because of your gender, then you are being sexist. A woman who wants to do business should not posit that a man is actively being 'sexist' if he chooses not to help her. That makes no sense.