The USPTO keeps a scam-prevention page for patent applicants. Its first point is that not everyone is eligible to represent you before the Office, and it warns against services priced too good to be true and firms that promise too much or cost too much. Each check below uses an official, public source.
1. Check the register, not the website
The USPTO's Office of Enrollment and Discipline maintains a public register of active patent practitioners. Only registered patent attorneys and agents, and individuals granted limited recognition, may represent patent applicants before the Office, and the USPTO says people who are not on the register are generally unable to represent others in patent matters. Search the name exactly as given, and be suspicious of any excuse for why it does not appear.
2. Ask who signs and whose name goes on the filing
On the trademark side, the USPTO warns about filers who use a licensed attorney's name without the attorney's knowledge, or who pay an attorney for the use of a name while the attorney takes little or no part in the filing. Ask the same question about a patent filing: which registered practitioner will sign my application, and what is their registration number? Then verify that number against the register. Treat evasion on this question as disqualifying.
3. Look up the discipline record
The USPTO's Office of Enrollment and Discipline publishes its final decisions, and the USPTO points to them for information about practitioners who have been disciplined. Private discipline is confidential, so a clean public record is not a guarantee, but a published exclusion or suspension answers the question. A practitioner with a clean record will not mind you looking.
4. Treat guarantees and pressure as red flags
The USPTO's scam guidance, written for trademark owners, describes the pattern: messages that pretend to come from the USPTO, pressure to act immediately, demands for fees that are not due, and official-looking notices from private companies. The USPTO also flags suspicious solicitations from non-attorneys offering patent renewal services. No one can promise that a patent will issue; the USPTO decides that. USPTO website addresses end in .gov, and emails directly from the USPTO end in @uspto.gov, so treat an official-looking message from any other address with suspicion.
5. Know where to report, and act quickly if you were scammed
A grievance about a registered practitioner goes to the Office of Enrollment and Discipline in writing, by mail or at OED@uspto.gov. A complaint about an invention promoter can be filed with the USPTO, which forwards it to the promoter and publishes both the complaint and the response. Trademark scams go to TMScams@uspto.gov. If you have already paid a fraudulent service, the USPTO's checklist for trademark scam victims covers the first steps, including a complaint to the Federal Trade Commission. Deadlines on a pending application keep running regardless, so have a registered practitioner look at the file promptly.
This section of Patent.org tracks official enforcement in this space: OED final decisions, exclusion orders, and the administrative actions the Office takes against fraudulent filers. Everything reported here comes from published public records.