Car sales — unsavory callers?

Hello dear MT community, I have posted my current car (Opel Astra-H Enjoy, 1.6 TP) at the usual car exchanges. Now on the first day several calls with offers came. These callers had a more or less strong accent. Also immediately came the price negotiation on the phone. A special caller from Poland made me without big negotiation a good price and he would pick up the vehicle Do. and Mi. should log off the car. Payment should be “cash” and i n €. Well, the whole thing is too fast for me and doesn’t seem serious. He’ll call again tomorrow if I’ve logged out the car. He said he needs to know that so that he can arrange the pick-up (it’s probably just Do. with other vehicles). He also said that I can bring the money to a bank and have it checked. Other special remark from him: “Can we write another (less) amount on the purchase contract?”, however, after my hesitation also directed s I’ll tell him tomorrow, however, that I didn’t log off the car and will still wait. He hasn’t got my address yet. I’m just afraid that there will be more such offers. Greetings, Sebastian