"Waiter, could you recommend something?"
Translation:Tarjoilija, voisitteko suositella jotain?
This is not the formal you. This the "communal" plural which exists also in English. You are just unable to spot it in the 2nd person plural, because English has only one you. You can however see it in the 1st and 3rd person. For instance, when a waiter says "My apologies, but we're out of lemons", or when you say to your friend "Let's go to that restaurant: I hear their sushi is really good". If you don’t do that it would sound like the waiter owns the lemons (and the restaurant). If you use the singular in the sushi example, it means you were talking about a chef earlier, not the restaurant. This is also why Finns talk to people in service professions using plural forms. It's not about being formal, it's just acknowledging the way restaurants work.
So, if you want the waiter's personal recommendation use "voisitko". If you want to the waiter tell you about the whole staff's recommendation, use "voisitteko". :)
Usually people want the recommendation of the chef or the kitchen staff when they ask the waiter this. Often even if you ask for the waiter's personal recommendation, they answer with what the chef and kitchen staff thinks. I realise that this sentence is very confusing though, so I doubt that it makes into the next version of the tree. :)
That would mean "Waiter, would you be allowed to recommend something?". When you combine saada with the 1st infinitive form of a verb, you're asking for a permission. voida, on the other hand, means "to be able to/to have the ability to". If there's no other verb with saada, it's often means with "can get", and in the conditional it's "could get", although English usually prefers "can have" and "could have". The -isi- between the stem and the personal endings marks the conditional, so in most cases it's translated with "would". But since Finnish does not have a modal verb like "could", that can also be the best translating in some cases. You can read more about the conditional in the Tips for Restaurant. :)