You should disclose everything you can about the site, including the tecnological aspects.
That said there may be items that you feel are your "secret sauce" then let users know that if they want that information, they need to DM you or you will tell them what you do generally and then tell them you will provide all the details/contacts etc. post sale.
Comments
Do the buyers care about the technological aspects of the website? What i mean by this is, do they buy websites that aren't written in PHP?
You should disclose everything you can about the site, including the tecnological aspects.
That said there may be items that you feel are your "secret sauce" then let users know that if they want that information, they need to DM you or you will tell them what you do generally and then tell them you will provide all the details/contacts etc. post sale.