You might suggest that they reduce the mass of beans that they are trying to roast. Most of the home roasting appliances are somewhat under-powered which makes it hard to get good results.

The other option is switching to the Whirly Pop on a propane camping stove. The cost of the equipment in that case is very low, especially compared to some of the expensive counter top appliances. I roasted hundreds of pounds of beans in the Whirly Pop and had just a few failures.