Most builders quote low to win the work and surprise the client when reality intrudes. We've seen what that does to projects, to relationships, and to final outcomes. So we don't do it.
A realistic budget is not bad news. It's protection. Protection for the project, for the client, and for the relationship that has to survive the build. Better to know what's actually possible at $X before drawings begin than to discover it after the foundation is poured.
We prefer clear expectations and disciplined planning before commitment. The math always reveals itself. We'd rather it reveal itself in the conference room than on site.