Can a customer or reseller be sued?
Section 271(a) covers unauthorized making, using, offering to sell, selling, or importing a patented invention, subject to its terms. A defendant does not avoid the statute merely by calling itself a reseller. Whether the particular product and activity infringe still requires proof.
What if the product came from an authorized source?
Under Impression Products v. Lexmark, an authorized sale exhausts the seller's patent rights in the item sold. Confirm the relevant sale and authorization; purchasing from a supplier does not by itself establish that the supplier had permission under the asserted patent.
What should I do with a notice or complaint?
Collect purchase records, the supplier agreement, and the identified product versions. Follow contractual notice procedures and ask who will manage the response. Keep court deadlines on your own calendar while supplier coverage is being resolved. A contract claim against a supplier and the patent claim against you are distinct issues.