For this one, provide a professional response to any questions, answering them if you can or pointing him in the direction of the answer if it is long winded or a complicated response.
- If the question directly links to your sale then obviously answer it.
- If it is a broad question like "how do i do SEO?" then point them at insightful articles or links.
When you sell your next website as somebody mentioned before, create simple documentation that helps the buyer navigate his new website, answering any questions you beleive he may have (also this first sale will provide many questions you didn't think would be asked ... so include them in your documentation)
Here's a little tip from me
Often with brand new sites, the buyer will be extremely new to the whole "game", because there will be a lot of questions, inside the documentation i include affiliate links to various ebooks or services.
New website buyers often need web hosting, so either provide them with web hosting or you can provide an affiliate link/coupon for something like hostgator.
By providing these
useful affiliate links in the free documentation you provide, new website owners appreciate the effort and help and often buy via your link - i can often double or triple my profit on a single sale just by doing back end promotional work like this.
Also, create a mailing list of buyers - These guys have bought from you before, theyre willing to part with money and if you have provided a great post sale service are willing to look at any marketing emails you send! ... Which means future $$$$$
Hope thats helped a little.