If it's in their background, 100%.
If it's up to the GM only, it depends on how much the GM wants to stop the player from being cool and using their abilities.
Maybe. It depends entirely on the character--and, of course, what the GM was like.
I, Faolyn, did not take a background that gives me an ability to call in favors. And I am far more of an introvert than the typical PC with a sailor background would likely be. Therefore, this comparison is pointless.
No, actually, you just failed to understand what I was writing.
Mamba said "so you agree that the sailor would not know any ship on the south sea when he ever only worked on the inland sea?"
I replied with "Wouldn't it be more logical to say that the sailor wouldn't have worked on any ship in the south sea?" and then went on to talk about famous ships and things along those lines. Things like "Oh, everyone has heard of the famous Imperial ship the Squidsmoosher!" I will admit I didn't outright say those words, but considering I talked about transmission of information via magic, so I think I was pretty clear.
You, somehow, took that to mean specific types of ships, like longships versus cogs. The goalposts stayed in place; you just wandered off in a completely different direction.
Chili isn't a ship and the Sailor background doesn't say you only know about ships in a specific location. You decided to add that and then treat your own homebrew as Official Rules.
Or, to put in D&D terms, it would be like having a background that says "you know things about other countries so you can roll blah blah in order to yadda yadda" and you took it to mean "you know things about one other country that happens to be right next to yours because there's no possible way you would know anything about a country on the other side of the ocean," and then insisted that your interpretation was the only correct one.