VintageRacer - the second point.
In many states of the USA:
Even racing for trophies would make you commercial.
Same for rodeo events.
Selling "whatever" at flea markets, etc. would make you commercial.
How strictly enforced?
A lot depends on the city, county, state - and the LEOs for same.
As well as any commercial "indicators" on your bus or race car hauler.
BTW - taking your friend's car to an event = commercial.
LEO's have been known to watch "events" and check those departing same for appropriate DLs, etc.
Reciprocity would apply *if* you were doing "whatever" within the limits of your home state (or province, country) Driver's License.
****However, things could get sticky doing "commercial" stuff w/o a commercial license.
Suggestion:
Run your question (PM or?) by "Big5er" on the Escapees HDT forum - or look at his posts/replies to/on that subject.
(He's very well informed due to his employment)..;)
.