I wouldn't worry about it.

If you are somewhat afraid of dealing with Americans, first think what you would do, what you would say if it's a situation where the other party is Chinese?

Then translate that into English.

心虚 seems to indicate that you are thinking less of yourself. Again it's a business deal. Do you think those car salemen would feel much 心虚 when they quote you a ridiculous price? Of course they are on the other end of the spectrum. Hopefully you've got my point.

You can either try to deal with it case by case, or you can brace yourself up mentally and be stronger in any situations.