I'm also wondering about liability, though not quite in that way.

First, what If something happens to the package that I'm carrying? I'm not going to carry something if I'm going to be liable if I break it, that risk won't be worth the gain.

Second, are the people carrying stuff for you going to be classified as employees? I don't know much about tax stuff but if you run the risk of the IRS classifying all these people as your employees, you might be running into a lot of administrative and liability problems.