Sale with deposit by bank transfer

Hello together, I’m just selling my old car. (for mobile for 2.5 inside). Get a call from a German mobile phone number – there briefly talked about the condition and agreed on 2.3 with the addition that there is not much negotiation on site. He wants to send a transporter from Lithuania, who picks up the car and pays 300 euros by bank transfer for my safety. He has also sent me his data and a photo of his passport. I want to remove the signs on the day of collection and only give him the letter (he meant that would be fine for him) and register the vehicle the next day. But I have read a lot of negative things now (but everything with any forwarding contracts and similar. He also wants to send the pick-up authority with him to sign the KV. Do you think this is serious? I mean if I have the transfer and get the rest in cash on the pick-up day is all right. Thank you for your tips in advance!