You ask "...Any thoughts on my decision making process?..."
Yes. It s*%ks.

"....When they sent us a proposal, they specified two coats of their
sealant..." "....When workers came, they acted all surprised....the
"manager" ... tried to convince me that I do not need two coats..."

These guys are robbing you, plain and simple. They charge for two
applications, but only deliver one. React accordingly. Life really isn't
all that complicated in most cases. Don't over analyze.

JG