There are 2 exceptions for Ping / Resell Notifications:
1st: Previous Owners - I allow ping/notify requests from the direct previous owner of a design I own (the person I get the design from).. Example: I acquire a design from the 3rd owner of a design. "Owner 3" may ask to be notified first if I decide to resell in the future, but the owners before them cannot. It stresses me out trying to think of who to contact first/what to do if multiple people say they want to buy it back (assuming I'm looking for basic resells). Why do I allow previous owners? I frequently buy emergency resells so as a courtesy I offer the previous owner the freedom to ask.
I have been in the situation of regretting the sale of a design and would have loved to have been told the new owner was not connecting, so I make that a priority for my ownership.
2nd: Original Designer - if asked to let the original artist know I usually allow that, too
