That is the peril of time and materials jobs---
The only way to avoid the 'sticker shock' is to keep up on the paper work---
Bill the materials every few days---never go more than a week for labor payouts---
Generally,T&M sucks---learn to bid a job and design one---I do have a few T&M customers--but they have deep pockets--like to make changes as the work progresses--so bidding for them is useless---but I collect my payments promptly--
Major purchases are paid for by the customer---
Good luck---
The only way to avoid the 'sticker shock' is to keep up on the paper work---
Bill the materials every few days---never go more than a week for labor payouts---
Generally,T&M sucks---learn to bid a job and design one---I do have a few T&M customers--but they have deep pockets--like to make changes as the work progresses--so bidding for them is useless---but I collect my payments promptly--
Major purchases are paid for by the customer---
Good luck---