Renting out your home or car for extra cash could leave you in a lot of financial hot water with your insurer.

I've talked in the past about sites like VRBO.com, HomeAway.com and Airbnb.com as way to get a deal if you're looking for a rental, but also as a way to supplement your income when you're the owner of the property.

But what happens if your place is damaged? I took a call some time ago from somebody with $50,000 of damage from their renters. The question becomes, who's liable? The owner's insurance disclaimed responsibility because it was not an authorized use of the property and was not allowed under the homeowner's policy. Ditto if someone get hurt on your property when you're renting it out on sites like VRBO, HomeAway and Airbnb.

The insurance industry has not caught up with the realities of what's starting to take shape in the marketplace. These sites need a system where people who rent through them have a way to buy coverage that covers the property for temporary use as a rental.

Meanwhile, on the car sharing front, I've talked about RelayRides.com, a service that lets you be a one-person car rental agency. But what happens if somebody rents your car and has wreck? Again, you're often not covered for commercial use of your vehicle, according to most insurers.

Recently, there was a terrible accident with a RelayRides rental. The question is who will be out of pocket? To its credit, RelayRides provides $1 million in coverage, but that won't be enough in this case because the injuries and damage were so extensive.

Again, the system needs to adjust. This kind of renting is a smart idea for people with idle cars and idle homes. But the insurance industry has to come up with business models that accommodate this. For now, you're a pioneer if you do this, and you're sticking your neck way out there in some cases.

The industry is simply not prepared. There should be a rider on insurance policies offered to account for this renting, where you pay more for the ability to rent your place or rent out your car.

In the meantime, especially if you rent out your car, there's definite risk if you have a lot of assets like a home and money in the bank. On the other hand, if you don't own a home and you have few assets, this might be a way for you to generate extra cash on your idle car.