The rule first, because it expires fast.
The person who greets you at the model home is a licensed agent working for the builder. Most Lincoln builders require you to register your own agent on your first visit, and they enforce it. Sign in alone and in a lot of communities you have just spent your representation on that entire neighborhood, permanently, before you ever picked a lot.
Bringing me almost never raises your price. The builder budgeted the commission before the model home opened, and walking in unrepresented does not hand you that money back. It just means the only person reading your contract works for the other side.
So tell me which communities are on your Saturday list. I register ahead of time, and nothing gets lost at the door.