This is a really bad idea for reasons already mentioned in other comments. Personally, I travel a lot and there's zero chance I would ever take someone's random package.

I think you should instead think of this as a B2B2C type business. As in, Business (You) helps Businesses (B) find people (C) that would help deliver freight packages. Even then, it's not really clear why UPS or DHL or whomever would trust a random person in their car vs. their sophisticated logistics networks. If there is some gap in their network, that gap is your sales opportunity. Maybe last minute things? Urgent packages? Etc.