I believe if you will provide your buyers a remarkable service with quality and good reception then they will surely get back to you either you’ll contact them or not!
I have a client who not only came back new projects but he told me he has recommended me to others in his field because of the quality I am delivering. I dont mean to brag here because I am also just a seller like you but what I want to convey is that you need to deliver your clients with dedication so they don’t go to anyone else after the order.
Also I don’t think staying in contact with your buyer after the project is a wrong move but I guess asking for another project is pretty lame and annoying!!!