How does one politely decline an internship or a job offer owing to new avenues opening up?
Has happened to me in the past where I was offered an extended assessment internship at a firm when I already had another internship planned for next month, so I had to lie to the other firm and give them a BS reason for not being able to join.
Was wondering if there are better ways to tackle this?

Lie lie and lie, they would do the same to you

I agree. Just lie and state personal reasons preventing you from going. There will be plenty of others who will take their place and life will go on.

Just say you have already accepted an offer from the next place.

Say, "I will get back to you" and don't. Haven't we heard this before?

Bump! What if I have accepted an internship but later get an offer from a much better place? I want to reject the internship offer after accepting it. How can I do the same?

Someone please tell this!

Been there done that. I rejected the offer stating that shifting to another city for a month would become too costly given the financial situation of my family - which was kinda true at that time.

+1, did the same thing. Was a great opportunity but shifting wasn't what I wanted to do.

but why did you accept the offer? You must have already known that u had to shift.

Bump. I have a standing internship offer for the month of March but now I have got acceptance from a better place. What is a good excuse to reject the previous offer?