When you are selling a directory usually you mention that the new owner should keep links and sponsored link intact. Is that enough guarantee for the advertisers? Shouldn't you at least inform your advertisers that you sold the directory? And when an advetiser asks you why you removed the link, is it OK totell him that you sold the directory, the new owners removed them and that you will remove his links also? Do I care that you remove his link?
People submit to a directory terms and conditions not it's owner, if a new owner wishes to change these terms and conditions it is beyond your control. A polite note to all subscribers saying you have sold the directory and thanking them seems polite and could save many questions should the new owner upset things to much.
And is it OK that he tells you that you should ask the new owner why he removed your link without even mentioning who the new owner is? That's an irresponsible way to do business.
I guess as a minimum a directory owner could email all past customers to let them know whats going on, then the new owner email those same people with an introduction email. In rare cases you would probably have that happen plus the new owner going out of their way to get to know the clients and maybe even do some special offers, but this would be very rare. I guess it depends on the circumstances and the intentions of the seller and new owner.
If any advertising is on a monthly basis, the new owner will need to contact the advertisers and have new payments set up. This also allows the advertisers the opportunity to continue or decline. If prepaid, you can only ask and hope the new owner will honor advertising till it expires.
Or refund if you sell the directory before even half of the paid period. The guy I am talking about didn't even cancel my subscription of 6 months or transfer it to the new owner, I figure this out when I got the cancellation because I didn't specify a new credit card in my paypal account.