Above is a fair response, however my advise would be before deposits are paid to do a little homework on the company. How long have they been trading? Are they Limited? VAT registered etc, this can all be done by simple searches online and will show you if they will be able to held accountable. Also avoiding cash as there is no trail of evidence of payment. Then ensure you have a contract or specification of works with the deposit being paid, deposits should never be more than 25% of the contracted works.
It would depend on the job being done
If there is a lot of materials required to be ordered it is normal for these to be paid for when ordered or the cost of returning if job does not go ahead.
If you are not ordering a large amount of materials then you would not expect to pay any money up front