Mortgage brokers, mortgage agents, and mortgage lending

How many times have you heard of a friend upgrading to a house and having difficulty selling their other home? Well, I forgot to share this information that I keep hearing. The market is bad here in Colorado just like everywhere else and a couple of people have shared with me their experience. They had their residence that they were trying to sell because they were upgrading or moving to a different location. Well, their previous residences were on the market for six to eight months without so much as even a glance. Consequently, the new homes they were purchasing became ready for them to move in. Both ended up renting the properties, but one of them is renting for six hundred dollars less than the mortgage. What happens then? They end up paying the difference for that home. Ouch! Talk about costing an arm and a leg, as well as paying on a new mortgage. As a broker or lender, what would you recommend to my friends?