When is it OK to pretend you understand Finnish?

If I dress appropriately and don't make a series of American gestures or sounds, some Finns will assume I understand Finnish. Which is a great feeling until you realize that what they are saying may be important to your finances or safety. But sometimes it is OK to pretend to understand. See if you agree with my decisions in the following situations taken from my life here:

In the grocery store, a short, elderly woman looked at the bags of potato chips shelved high above her. She stood on her toes and reached her full length to get one of the bags. Once she got her bag of chips, she turned to me while chuckling and described in length something funny that obviously involved potato chips on high shelves. Would you have pretended to understand Finnish?

Me: I pretended to understand everything she said and chuckled with her, nodding my head, glancing at those bags of chips high on the shelf, while rolling my eyes. We had a good laugh together.

My justification: Potato chip bags high on shelves where short, old people (like me) can't reach them actually is funny (to tall, young people). The nice woman just wanted to share this moment with me. She walked away, still chuckling, and that stranger who "understood" her plight made it more bearable to be old and short. Or maybe I unknowingly agreed that she should shop elsewhere farther away. Oh well, no harm done; exercise will be good for her.

At the department store I was buying a few items and using my basic, common Finnish: hei, joo, kiitos (hello, yes, thank you) as usual. Suddenly the sales clerk stopped the transaction and asked me something at length. When this happens I usually say "joo" (yes) just to get out of the situation. Would you have pretended to understand Finnish?

Me: I quickly marched out one of my most useful Finnish phrases: Anteeksi! Puhun vain vähän suomea (Sorry! I only speak a little Finnish).

My justification: This is a tricky situation. At this point a sales clerk will often be asking whether you want a bag or want your receipt. Saying "joo" (yes) quickly finishes such transactions because you usually want either a bag or receipt, and you preserve your charade of speaking workable Finnish. However, you need to be careful here! When I confessed my Finnish was limited, I was able to stop from being signed up for a new credit card for which I would not have qualified.

On the tram, a disheveled and intoxicated man sat next to me and started talking. He was not threatening in any way, but he was obviously anxious to give me his opinion on a topic that only he knew about. He was not whispering, either. Would you have pretended to understand Finnish?

Me: I pretended to understand everything he said and made signs of agreeing with him on every point (head nods and positive "hmmm" sounds). After a few moments he seemed happier, and then he went on to another captive passenger.

My justification: Most drunk people do not strike up conversations with strangers in order to get into an argument. Rather, these people simply want a sympathetic conversation where you confirm whatever they are saying. It may be one of the rare times when someone actually agreed with him. Perhaps this positive experience convinced him to mend his ways. Or maybe I unknowingly agreed that he should drink more. Oh well, he probably was going to anyway.

It is obviously a case-by-case judgment on whether you should pretend to understand Finnish. You just have to weigh the options and, if you pretend, be prepared to live with the consequences.