Always take a deposit, especially if you are supplying tiles, I've been kind enough to negotiate a discount for the customer to help them, so they have to show some commitment back to me.
When it's supply and fit of kitchens then it's a 50% deposit, without any exception.
I don't order anything until either the cheque has cleared or the bank transfer has gone through ok.
Makes business sense, too many companies go under because of cashflow problems. You only need one bad/none payer and it causes major problems i.e. time and hassle to retrieve the monies owed, and the the stress related to it.