High deposit asked for before starting job - is this normal?

It depends on the cost of the materials and fittings really. I know a lot of people want the materials bill paid before starting work so, although there is a possibility of losing time, they are not losing money as well if the customer doesn't pay.
Ask him what this figure represents, make sure he gives you some sort of written contract/receipt and look into his reviews.

70% is a bit cheeky to be honest I usually ask the clients to get the materials so when I have half the work done I get half the labour cost and the rest when I finish this way if and it does happen a lot if clients don’t pay iam only out of pocket for my time and not for materials aswel but 70% upfront is risky try come to an agreement we’re you buy the materials and you’ll pay half the labour costs when his half the work done and the balance when finished and your happy with the end result