Using a sub-domain to sell a name

How would potential buyers arrive to the sales page on sale.trafficroller.com ? If the buyer contacted your whois email, then there is no need to maintain anything on subdomain. If the buyer/visitor did not contact you directly, then what would prompt them to type-in a specific subdomain in their browser? Or did I misunderstand the whole scheme?

The closest thing I am thinking of is:

IF (and only if) the domain has _expired_ traffic - then some visitors would click on old links - and such visitors may be well detected as their HTTP referer would not be empty. So it may be possible to serve variable content right on www.trafficroller.com / trafficroller.com . Visitors with non-empty HTTP referrer are less likely to purchase the domain as they simply clicked an old expired link. Forward them to appropriate affiliate link or to traditional parking company in above.com traffic management style (to for example ww3.trafficroller.com which has dns cname record pointing to a normal parking company server). Those visitors of www.trafficroller.com / trafficroller.com that have an empty HTTP referrer are probably direct navigation visitors, so they may be interested in purchasing the domain, and "domain for sale" page is generated for them, not a forwarding code....

That was the major stumbling block. That's why I asked if there was an industry standard, so people could check for a sale sub-domain. The other alternative is to include it in the who is info.
One other possibility is to use a page that will get indexed by Google, so it turns up in the SERPs.Of course one would list it on one's own sales listing pages.

Use a sub domain and place a link to it in the header of the index.
Buy this domain and a link