The most important thing a seller needs to know about IP complaints is to immediately address any complaint you receive.
Don’t let it linger on your account; they do not go away by themselves. A seller needs to get an appeal or reach out to the rights owner for a retraction so that your account does not get / remain suspended.
One of the biggest problems that sellers face is that they reach out to the rights owner or brand and get no response. Using an experienced law firm such as Rosenbaum Famularo, PC, the firm behind AmazonSellersLawyer.com is helpful; lawyers tend to get better results from the complainant than the seller.
You never know when Amazon will finally suspend your account for IP complaints; larger accounts can withstand more complaints than smaller accounts, but there really is no specific number of complaints required for IP suspension.
If a brand does not respond or refuses to withdraw their IP complaint, you can reach out directly to Amazon at Notice-Dispute@Amazon.com and create a Plan of Action letting them know that you have unsuccessfully tried to contact the complainant; therefore can they please help you resolve the issues on your account.
A Digital Millenium Copyright Act (DMCA) counter notice can be used when there is a baseless copyright complaint made against a seller. It gives them the ability to tell the brand that they either have to sue or drop their complaint.