There is a small chance they send someone over to check. They normally show up between 9-5, so if you're at work, chances are you'll never see them to let them in.
If you are home and they knock, you don't have to let them in. You can politely tell them to leave.
Or you can show them your TV and that it's not hooked up to an aerial. They'll ask if you use iPlayer, you say no and they leave you alone.
Source: lived in the UK, never paid for TV license. I let them in once to see what would happen.
(I lived on the Isle of Man for a while, and the local newspaper would be alerted by the ferrymen when the van was shipped over, and run a warning for everyone to turn their TVs off for a few days).
It's only easier to evade now because flat-screen TVs don't emit radio signals they can detect from the street.
If enough people opt out then they'll do what they do in Germany: everyone pays it regardless of whether you have a TV or not.
This one was amusing: https://www.youtube.com/watch?v=w_nRsnd2-Lo
More laughs here: https://www.youtube.com/@fu4nvf/videos
By my understanding, the BBC license fee is only required if you get television service, if not you can opt out.
You'd think if someone was unable to heat their home they wouldn't be paying for TV, and thus wouldn't have to pay the BBC tax either.