Yep, ask for your deposit back and find someone decent.
Full payment on satisfactory completion of the job only.
The fact that he can’t secure the materials on his trade account with the supplier stinks.
totally agree, worked for a chap a few years ago, he had just paid someone up front to fit and supply new guttering and down pipes, they called round while we where there asking for cash to buy materials, he gave them a few hundred quid and never saw them again.
If you like him and trust him offer to pay the supplier at the depot and get it delivered to your house, then pay for fitting when completed.Thats what we do.
or your payment may just be to pay of another supplier, also say you want your deposit back and see what he says.