Don't forget relative value to a Mr. J. To a Mr. J working for an AAA corp, 80k in runner expenses probably isn't worth getting in a tizzy over. Almost certainly not worth the actual expense of arranging for someone else to whack the team, be they internal or external to the corp., let alone the intangibles of potential failure, reputation hits, and flat out personal risk. 500k, a cool million? Maybe - but the type of guys you pay that money to are notoriously good at not getting dead, so really unless you violate one of the rules other people listed, a crop J isn't real likely to try and screw the runners. The value of the reward just isn't worth it. It doesn't mean you'll never get a hungry J trying to shave costs and he thinks he can get away with it, or he's using the runners to launder money to himself, or other personal scenarios, but these are the exception, not the rule.
Now, as you start sliding down the scale of available assets, the idea of killing or not paying the runners goes up in likelihood. If your an small seoulpa ring branch with your back to the wall, or your a gang that really needed that last shipment of BTLs to sell a lot faster and it turns out you don't really have the money after all, or your an up and comer with a lot of balls but not much money - or any other situation where 80k of nuyen can be a major issue - now the chance for a backstab over simple value goes way up. Because it can be a major coup to get the job done and the payment back, and is therefore worth the risk.
Especially if the organization has muscle, just not expertise. For example, a local tier 2 gang chapter may have more than enough go gangers to massacre you, a minimal cash flow, but a serious need to do something more discrete or technically sophisticated - infiltration, cracking, some mojo related shit, whatever.. Well, they know you gotta pay for what you get, and they need some first rate skills or they'd do it themselves, so they'll offer some yen, but the average runner team probably outprices what they're willing to readily let go of. And they do already have a lot of guys with guns who are comparatively cheap - troubled youths aren't that hard to find - so taking a crack at the runners seems pretty fair and balanced at this point, especially since its not like they have to hire runners monthly.