im new in UX, actually a prepare for first research. I read many material for user testing strategy and every says about determine scenario for task. Is this necessary? I think about. Would be more natural let the user himself decides for better, more realistic experience? For other hand results by more consistent. Have you any practice for this method? Do you see any problems with that?

Context: I redesign site for renting rafts and I do not know if I should determine under what conditions (price, number of people, ...) should participants are ordering rafts

Thanks for your response! Matúš

I've read material about user testing strategy and they all talk about determining a scenario for the task. Is this necessary? 

Wouldn't it be more natural to let the user him/herself decide on the better, more realistic experience?

On the other hand, having a set scenario would mean results are more consistent. Have you any practice for this method? Do you see any problems with that?

Context: I am redesigning a website for renting rafts and I do not know if I should determine under what conditions (price, number of people, ...) should participants are ordering rafts