Normal has quite a few variations.

While this group often discusses contractors cheating customers, plenty of
customers wil cheat the contractor too. getting an up fron deposit is not a
bad thing. Maximum is usually 1/3 on large jobs, 1/2 on small jobs.

Larger contractors can buy the materials and pay for the labor, but many
smaller, honest, reliable contractors just don' thave the resources, or will
have to pay a bank for money. In the end, the customer ually pays more in a
case like that.

I just got three bids on a job from seemingly reputable contractors. There
terms a
#1 1/3 at signing 1/3 at half completion 1/3 at completion
#2 1/3 at signing 1/3 at start 1/3 at competion
#3 no deposit total due at completion

Very long and involved jobs often require payments along the way. If so,
they should be spelled out and agreed to up front. They may be broken down
to a payment at: signing, delivery of certain materical, completion of a
certan stage, delivery of more material, etc.

In no case should you pay the full amount before completion.