As the agent took the deposit from you directly, there is a high probability that he is playing a common double contract game. That is to say, he has one price agreed with you (the marketing price) and another lower price (the net price) agreed with the seller. Of course, the only way to get away with this is by claiming that the seller needs black money.
Another very popular, and very profitable, game is for a supposed agent to sign an exchange contract with the seller with a long delay before completion – say three or six months. The agent then sells the property for twice as much by pretending he is simply an instructed estate agent.
All of the profit then goes straight into his pocket and the taxman is aware of nothing as his name appears on no official documents. Pulling off this stunningly profitable trick requires naive and trusting buyers and sellers who are happy to ‘save’ on their taxes by using black money.
As the agent was not able to supply any headed paper for a deposit receipt I would suspect that he is trading illegally. He may try to cover his tracks – and add insult to injury – by offering you the opportunity to save VAT by paying him in black money too.
Did you obtain any references or find any background information about the agent?