Once the brain draws a conclusion, it immediately starts looking for proof that it's right.
Remember being convinced there was a monster under the bed?
Every shadow confirmed it.
Every sound made it more real.
Nothing changed.
Your client does the same. If the first impression is good, he'll notice every detail that confirms it. If it's bad, he'll find reasons to leave.
It's not just what you communicate that matters. What matters is which belief you confirm in the first few seconds.
Confirmation Bias