they are a business, if they need your money to cover the cost of getting the parts in stock then they are not worth dealing with.
only ever leave a small deposit and get a recipt for it. once the parts are in stock and your ready to pick up then pay them money.
99% of all stories I've heard/read about people getting ripped off is because they paid upfront.
Yep, I'll 2nd that thought.
I've had friends who have been fucked in the ass coz they payed upfront.
Once they have your money, they couldn't care less how long it takes them to do it.
And if somebody else who comes in spends more money than you, their job gets a higher priority than yours