What a seller sees is your brief: what you want, any constraints, and whatever context you attached. They do not see your other quotes or what you paid anyone previously.

A brief that gets useful quotes names the outcome rather than the implementation, says what already exists, and states the real constraint — a date, a budget ceiling, a stack you cannot leave. "A booking form that writes to our existing Postgres, live before the 12th" produces better quotes than "a booking system".

Reading the quotes. They will not be like for like, and that is normal. Check what is actually included: revisions, deployment, whether the price covers the thing running in production or handed over to you to run. A cheaper quote that stops at handover is not cheaper if you cannot deploy it.

Deciding. You are not committed by asking. Quotes expire, and you can go back and forth on scope before anyone starts.