Years ago I looked into doing ad hoc courier travel, as I'd occasionally courier whilst in the military. But IMO too many restrictions, insufficient benefits.

Ad hoc couriers who got cheap tickets for their "services" (usually the baggage allowance, which they never actually checked or retrieved,) used to be fairly ubiquitous, but their use has diminished significantly. The use of DHL, FedEx et al, specialized couriers carefully selected for special cargo (diamonds, etc.) have supplanted the large number of ad hoc couriers.

Those like Bozza are known entities and are usually repeat well known pros or semi-pros. Ad hocs generally didn't receive many of the fees and perqs these reliable and trustworthy people get.

Otoh, there are more volunteer couriers for rescued pets, goods for NGOs, etc. but their courier duties are ancillary to their fully bought tickets. E.g. as a lifetime member of South American Explorers I have volunteered to transport goods to one of our Clubs - usually Buenos Aires, Lima or Quito, when I'm going there because I usually travel with carry-on only, but have a usual checked baggage allowance of four 70 lb / 32 kg bags as long as I'm flying a oneworld airline.