Yellow Card

Whether it´s compulsory depends on where he is flying, where he is transiting and sometimes even which airline he is flying with. For example, if he is flying via Panama a Yellow Fever certificate is still compulsory.

Just to begin - no, aguas, I don't have issues - well, only issues with the ridiculous things you write. Change the record, yours is broken.

In Ecuador bribing is the way to go.

What a brilliant attitude - keep that corruption nicely entrenched and encourage officials to expect bribes from foreigners. Really ethical and responsible. That's how we're going to eradicate corruption, isn't it, by encouraging visitors to throw cash at officials to get out of their (legal) obligations. Brilliant.

I agree polyglot55, and in any case, attempting to bribe an airport border official would be utterly stupid, especially for a foreigner. Those days are long gone in Ecuador. The anti-corruption drives have hit hard and staff are constantly monitored on CCTV now. They aren't going to risk their job for $50, but it will land the OP's friend in jail if/when they are reported.

This is completely ridiculous, being required to present a YF card to fly back to the U.S. And it certainly wouldn't cost $500 to "process" it. The card is necessary only if you have been in a country where YF is endemic, and are traveling to another country that requires it (Brazil, Bolivia, and Australia come to mind). The U.S. most definitely does not require the vax. You can get the YF vax for free at a public health clinic, and the card will cost $10. You receive it immediately--there is no "processing."

It really sounds like the official was corrupt--CCTV be damned--and was hoping to scare a gullible traveler into paying up.

That's a good point azbuceadora. I was assuming the 'processing' fee would be an airline fee to reroute through another country (since as you say the US don't require the vaccination). But reading it again the OP says immigration, so maybe not, or perhaps wires have got crossed somewhere. It's more likely they would try and tap someone for $500 than $50.

Sometimes I have passengers who leave Ecuador to Costa Rica. In this case the airline is responsable to check if any passenger has a yellow fever certification. If you don't have one they don't let you enter the plane with the argument that they have to bring you back in case that you are not allowed to enter Costa Rica. I never heard a case that custom officers or people from migration are asking for this. I think they wanted to make some money with this.