I have been working with a GAM model with numerous features(>10). Although I have tuned it to satisfaction in my business application, I was wondering what is the correct way to fine tune a GAM model. i.e. if there is any specific way to tune the regularizers and the number of splines; and if there is a way to say which model is accurate.

The question is actually coming from the point that on different level of tuning and regularization, we can reduce the variability of the effect of a specific variable i.e. reduce the number of ups and downs in the transformed variable and so on. So I don't understand at this point that what model represents the objective truth and which one doesn't; since other variables end up influencing the single transformed variables too.