That's the easy part. The hard part is getting them to cough up the money when the bill comes due.
That's what I meant with getting people to "commit" to the buy.
It is not usually quite like that. Most of the folks have no issue paying up front for the part. It is the fucktard sitting there with several grand in his pocket that is supposed to place the order who decides to take a vacation to Vegas with the funds and then goes radio silent. Then everyone gets on the vendor's ass who tells them to fuck off, no order was placed, then they go the forum owner trying to get him to find the fucker who spent their money and it goes downhill from there. The really bad part is some of those fucks have had the audacity to start posting a couple years later in hopes that folk's memories are shorter than the pain from being fucked. It rarely is.
There's gotta be a way to prevent that with an escrow of sorts. Vendor gets committed buyers, buyers rest knowing the vendor won't receive a dime until he ships the finished product.