Well, to back up a bit. I am not 100% certain as to the law of trespass in Florida - but most states' laws on trespass do not differ. Businesses that are open to the public are ordinarily deemed to have consented to any trespass (which in the legal sense is distinct from criminal trespass, which is what you are talking about) until the owner requests that you leave the premises. In other words, until you were asked to leave you were not committing criminal trespass and the police office had no business citing you for anything. At the very most, the officer could have told you that he had been requested by the owner to tell you to leave the premises.
Of course, to tell an officer otherwise on the scene is to dramatically raise the ante, and I'm not sure I'd suggest you do so unless (1) you are a lawyer, (2) you have some resources to dedicate to the fight and (3) you have no concerns about being outed. So you probably did the right thing by just moving on. But, unless there's a genuine peculiarity of Florida of law at play here, the officer was not acting properly.
I do not know the current state of Florida's discrimination law on gender presentation, but I do suspect that the "we reserve the right to refuse service" concept probably protects the owner of the flea market. So she did have the right to say "don't come back here" irrespective of HOW you are dressed. Your best recourse is to do exactly what you did: publicize the intolerant attitude of the owner and hope that social pressures eventually compel a change.
Standard disclaimer: I am not admitted to practice in Florida; this is only a general statement of my understanding of the law; this is NOT legal advice and you are not my client. Hey, I have to say this stuff.
By comporting yourself with dignity and decency in the face of idiocy and intolerance, you did absolutely the right thing. Well done!