If arrested, what should one say?

[Petros]

I doubt if they would need to prove a direct money connection to you. That could only happen if they recorded the handing over. I think other things would make it "beyond reasonable doubt", like:

- presence of large quantities of condoms in different sizes.
- presence of sex toys / special outfits etc
- presence of unusually large quantities of cash.
- evidence of multiple male visitors who stay for 30-90 minutes.
- evidence of appointments from phones and/or laptop

With a few of those I don't think you have much chance of getting off if you fight it. They will also make it clear that an unsuccessful "not guilty" plea will be worse for you.

If caught I think I would be polite, ask for a lawyer, and admit / deny nothing.

The evidence you list there would indeed be very damning in a court but it still does not "prove" someone has paid for sex.

All that proves is guilty by association. Suppose the lady has a friend visiting - someone who they know in their private life who is not a punter! If the only evidence that was required was that which you list then the friend could be found guilty of paying for sex!

The same as say a repair man who might find himself in the apartment could also be convicted of paying for sex.

I'm sure there would have to be other evidence required to secure a conviction so as to avoid such people being convicted!