Guide Locked in the Tavern before going to the EITC office.

[Jerdna_Stark]

I hope I labeled this correctly.
Minor spoilers I guess. This happens pretty early on in the story and there's not much here to spoil you, but still...

So I was playing through the Hoist the Colours storyline and got to that point where you've escorted Beckett to Port Royale and I had the bright idea of doing an escort mission to get some more money before going to the EITC office. So I went to the Tavern and arranged the voyage with the merchant only to discover afterwards that I was locked inside. The exit was literally locked and Fast Travel was unavailable. I tried to rent a room until the next day but it didn't work, the door was still locked and FT unavailable. To make matters even worse, I overwrote the last save file immediately after talking to the merchant so I was basically stuck there.

So if you ever find yourself in this position, here's how I fixed it:

Talk to the bar-maiden (the woman walking around from table to table) until you get the line with two dialogue options and agree to her offer. After leaving the room, approach Thomas Tipman who is standing amidst the tables and talk to him. He tells you about Barbossa and your QB updates. After that, you are able to leave and continue the story. This also skips the part where you go to the Office and Beckett isn't there; instead, he's there and you can talk to him, get paid and continue the story.
I'm not sure if this also works if you rent a room and I didn't want to take the risk of finding out.

 

[Grey Roger]

This is supposed to happen and is nothing to do with the escort mission. You escort Cutler Beckett to Port Royale, go to the EITC office and talk to Silas Simpkins, who tells you that Beckett is not back yet and you should go to the tavern. Inside the tavern, fast travel is disabled and the door is locked so you're not getting out again until you have talked to Thomas Tipman. The whole point is to force you to talk to Tipman, from whom you learn about Barbossa and the map.

Renting a room should be alright. Tipman should still be there the following day, and you're still not getting out of the tavern until you've talked to him.

 

[Jerdna_Stark]

This is supposed to happen and is nothing to do with the escort mission. You escort Cutler Beckett to Port Royale, go to the EITC office and talk to Silas Simpkins, who tells you that Beckett is not back yet and you should go to the tavern. Inside the tavern, fast travel is disabled and the door is locked so you're not getting out again until you have talked to Thomas Tipman. The whole point is to force you to talk to Tipman, from whom you learn about Barbossa and the map.

Renting a room should be alright. Tipman should still be there the following day, and you're still not getting out of the tavern until you've talked to him.

Ah, I see. I should have thought about that... Thank you.