usually if you can pay off something in a 3 year time span your doing good, 2 years is even better (at least that's my formula). I think pinball is a bit different, a routed star trek pro like this one he could turn around and sell for at least 60% value, if not more maybe. Almost every other piece of vending equipment usually drops like a rock in value by 75% or more by the time you sell. So, even if you don't get it paid back by year three, it's not the end of the world. If secondary market prices drop, then yeah it definitely won't make sense to route pins anymore or at least older pins that don't earn as well.
Not sure how much a star trek cost where/when he got it, but lets say we take the pinballs.com price which is $5495.
if he were to sell his machine for $3297 I'm pretty sure he would have a lot of takers.
now if he took really good care of it that number only increases.
it also helps take the sting out, if it's a hobby as well.