Once agreed to, a sales agreement is legally binding.
If we do not honour our part of the sales contract, we may either lose our deposit or be legally obliged to continue with the sale and hence pay the full amount.
We should negotiate with the trader the amount of deposit to be paid.
We should hold on to our money until what we have ordered is delivered and carefully checked out.
Very small deposits may be a marketing tactic to encourage us to sign an order without reflecting.