With all due respect Nino, I think the cavemeister may have some valid points.
The payment options may well have worked in the past but this is 2015 and you do have to move with the times. Paypal is great.. as a supplier it is even better. Anyone that doesn't receive their goods instantly can make a claim against you ( instead of talking directly). Paypal will instantly freeze your Paypal account and all its funds until you manage to get the buyer to email them and state categorically that they do actually have the goods. Signed signatures as proof of delivery are useless in this instance... only direct communication from the buyer will see your funds released a couple of days later.
Come on man.. move with the times!

Now then.. 4 year waiting lists for restoration work. Of course this is totally unacceptable. Only top end USA restorers have these kind of waiting times. Im sure I don't have to remind you that this is AUSTRALIA. A quick check of the world map on your part would address this issue.
So how do you cut down waiting times?.. Its very simple.
 You do need staff and a process to restore these machines. Once you have streamlined the process to a semi mass production level, then you wont have to stress over the quality too much. Substandard work is totally acceptable in this instance.
Take a look at Stern ( or even Toyota!).. they are massive and have been making machines for a few decades now. They have issues with the clear coat process, but remember... this is mass produced and as such we, the customer, fully accept that standards will drop once the process is streamlined. Stern are top of the pile Nino - you really should follow their lead my friend.
Owning the premises and all within it... very poor business move on your part. Again, we could take Sterns lead here and acquire a larger factory. The costs of this and the extra office staff can be directly passed onto the customer and remember, if you drop your standards a bit to move these machines out the door then its like making profits on profits! Win win situation!... what business wouldn't want to do that?

Business advice is given freely here and your refusal to adjust your model to suit says more about your personality than anything else. I am not kidding when I tell you that there are people on here who have made MILLIONS over the years and have bought at least 50 PINBALL MACHINES with the money!!... all at sub market value due to great business acumen.
How many machines do you own Nino? What price did you pay? Are you operating them 24/7 365 days a year? Are they making $10 trillion dollars a day for you?

All food for thought my friend...  don't choke will you?