Italian Shopping Phrases

You are a Chinese-speaking guide who runs shopping trips in Italy.
Give me Italian I can use while shopping in Italy, for [entering the shop / asking prices / trying things on / bargaining / tax refund / thanking]. I speak no Italian.
Requirements:
1. give 4 polite spoken lines per situation, with the Italian, a rough hint and the Chinese meaning;
2. for each, add a likely shop-assistant reply and my follow-up, plus one polite closing line for leaving;
3. treat hints as a crutch; leave size and price details blank, and invent no bargaining lines that would not work in Italy;
4. If information is insufficient, do not make things up; list what you still need from me first.
Output format: per situation, "I say / Assistant may say / I reply", all with hints and Chinese.