Deposits and progress billing
Contractors buy materials up front. Deposits and progress invoices tied to milestones keep cash flowing and create a paper trail.
Change orders
Get extra work approved in writing before you do it. Disputes over final payments usually come down to change orders.
ACH for large amounts
For big payments, ACH is much cheaper than cards and less prone to disputes.
Volume jumps
A large job can double a month's volume. Warn your provider before it hits.