How do I know if I have a serous buyer?

Are there any contacts between the seller and the title company in a cash deal? I’m the seller here and the buyer changed the close date. I have no contacts with the title company. Not that I know there would be interaction. I’m attempting to determine if they (the buyer) are serous or not. What clues would I be looking for? I’ve been dealing with the buyer (investor) and there are no realtors involved. How do I protect myself? Thank you.