Create Gmail Filters based on strings in the Doesn’t Have field

As an Ebay seller, I currently filter all e-mails from Ebay to a folder. I would however like to keep those that contain “sent a message about” or “buyer opened a request” in the inbox so I can address those quickly. Based on another question here, I tried setting the “Doesn’t Have” field as

(sent a message about) OR (buyer opened a request) 

but that didn’t seem to pick up the right e-mails when running a search. A lot of the e-mails that SHOULD be in that folder weren’t showing with the query…

to:(myname+ebay@gmail.com) -{(sent a message about) OR (buyer opened a request)} 

How can I set this to skip e-mails with those strings in the title and leave them in the Inbox?