I agree 100% with tecman. I think I'm a decent pilot with nearly 2000 hours, CPL-IR and all the rest. But no way am I taking a complete stranger up in my plane, whether for money or not. The risks if something goes wrong are just too awful to contemplate.
And similarly, I would be VERY wary of climbing into a plane flown by someone else unless I knew quite a bit about their piloting skills. If they have a CPL and 1000 hours, sure. 50 hour PPL - I don't think so.
The trouble is that this is all obvious if you're a pilot with a bit of experience. But the people who are jumping on this just have no idea - a pilot is a pilot is a pilot, just like those nice chaps up front on Ryanair. I think we've all been there in "oh sh*t" moments, when it's all going pear-shaped and it's a struggle to just keep aviating. But 50 hours PPLs haven;t yet had their share of this stuff. (And I don't consider myself seriously experienced, but at least I have seen how things can go wrong).
Luckily in the US it is very clearly forbidden - it is considered to be "holding out" and requires not only a CPL but suitable air carrier qualifications, the whole Part 135 ninety-nine yards.