mark625: Detained and deported over suspicion of attempted house sitting? In another country, even?

I don't understand why this is surprising. Without the proper visa this sort of thing is illegal in a lot of countries because it counts as work. That is why you never tell immigration officials this is your reason for or plan while visiting a country if you are arriving on a tourist visa; you always just tell them you are visiting a friend and staying with them for awhile. And you make sure your host knows this in case they get a call from CBP to verify your story. 

Despite that f*ck CBP. There is zero reason to ask a traveler about abortion.

/ have done Workaway in several countries; most don't care as long as you aren't getting paid, but some, like the US and UK count any exchange, even room/board, for work as compensation and so illegal without the proper visa

Stands With A Tiny Fist: Why does US customs feel entitled to be making Canadian visa decisions on our behalf?

Now this is a better question. I don't know if countries work out deals or if there is some risk or fear that the receiving country will be angry that someone got let through or what, but I've run into a similar sort of thing once in Japan where they wouldn't let me board a flight to the UK unless I also bought a ticket from the UK to literally anywhere else. I was flying to London in 2006 to start a bicycle tour of Europe from there and was planning to take a ferry across to the mainland, but immigration in Japan was for whatever reason looking out for British immigration and so wouldn't let me fly until I'd fulfilled the exact letter of UK immigration requirements. Probably because they didn't want to deal with tourists being flown back to Japan if they didn't satisfy the requirements.

Funny thing was, in the UK they didn't care about me having a flight out booked at all. I told the immigration person I was taking a ferry to France in a couple of weeks and that was that. No need of proof or anything. Luckily I was able to fully refund the ticket for a flight I was never going to use.

But something like that shouldn't hold for connecting flights and layovers. US CBP was probably just on another power trip, since there is absolutely no consequence for them going on power trips. F*ck CBP.