Just make sure you sign the "offer to purchase" or "booking form" when you pay the 2%.
Do not pay anything without getting something B&W in return that states how much you paid and why you paid that sum.

And never pay anything to the agent (except the commission). All deposit whatsoever should be paid in cheque issued to the seller.

If possible, demand the agent to arrange face to face signing session with seller. Pay and sign everything together.

Both buyer and seller have to sign, and usually I'll get someone else and sign on that form as witness as well...