Thanks everyone for the clarification!
Basically I've not been collecting money on this Freelance trips, I've been trading my photos for accommodation and some living expenses.
And the people I have been doing this are my friends so I don't think there should be a problem to mention that on the customs.
I always say I'm just visiting the country and visiting some friends but some officers just think it's weird that I'm going from one country to another by myself and make too many questions which make me nervous since I'm not sure about my rights