Yes, it is very possible that someone says it was theirs before you registered it.
It happens all of the time.
But normally it would be hard for someone to actually win such a thing. The trademark process is exhaustive. The USPTO does it's own search after you submit your application. This includes all state registrations of businesses as well as online.
If you make it past this hurdle, the USPTO publishes your mark and puts the general public on notice that unless someone comes forward to dispute the registration, that they will officially register the mark.
Once this happens, then it will be extremely difficult for someone to win a claim and get your registration revoked, though not impossible.
More than likely, once you get registered, you should be in the clear.
It happens all of the time.
But normally it would be hard for someone to actually win such a thing. The trademark process is exhaustive. The USPTO does it's own search after you submit your application. This includes all state registrations of businesses as well as online.
If you make it past this hurdle, the USPTO publishes your mark and puts the general public on notice that unless someone comes forward to dispute the registration, that they will officially register the mark.
Once this happens, then it will be extremely difficult for someone to win a claim and get your registration revoked, though not impossible.
More than likely, once you get registered, you should be in the clear.