I've been getting a lot of phone calls from users recently. I like it. My Revit people, calling me to talk about Revit Market.
One of the big questions that comes up is about liability. If a downloaded family leads to structural or cost errors, who is responsible, the creator/uploader or the downloader/user?
The answer has to be the user. It's the only way that makes sense. The user has the power to use the family any way he or she chooses, and to make changes to the family before using it.
Our End User License Agreement (EULA) specifically states that the purchaser, not the seller, is responsible for how a family is used in a design. The seller makes no warranty about the accuracy or usefulness of the family.
This is similar to the EULA you sign when you purchase software. The manufacturer actually states that they're not responsible for whether the software works. If it doesn't work, you would, of course, return it and expect a refund. What they're really protecting themselves from is you using the software in a manner they didn't intend or expect, or experiencing occasional software failure. (Imagine if you could sue Microsoft every time Windows crashed! What a different world this would be.)
Our EULA serves a similar purpose. We don't guarantee that the item will be useful for any one user, or even that it will work. We give refunds on non-working models and families, but you (and we) are not liable if the user doesn't bother to check a family's integrity before using it for BIM or building instructions.
At TurboSquid, we've been doing this marketplace thing for 8 years, and we've worked out all the kinks in the EULA. We've never had a single problem with this issue. So, go ahead and publish your families with impunity!