There are some excursion seller in the PDC harbour that are extremly agresive in their attempt to sell sth. Some just give out hand written notes and try to charge "a deposit". When you wait next day for the bus you realized you were cheated. Better go to the big offices that have all the tours, they are serious and offer the best prices.

If someone just approached you in the street in the UK to buy a trip out tomorrow, would you buy ?

So why do people do it abroad ?

and who said it was in the street??? They have small offices there in the harbour and pretend to be official, but they are not allowed to sell what they sell. They just try to do some extra money, and if you dont know that you wouldnt think its a cheat. If it would be a clear thing as por example "get a bargain in an electronic shop" I wouldnt even bother to write about it.