Customer Service vocab

Hallo zusammen! I work in customer service/tech support where I take a lot of inbound calls. Recently I was asked to come in earlier in the day and start taking calls from Germany and the UK. My German is definitely rusty but my main concern is the sort of verbiage I'll need to know.

My field is mobile accessories/consumer electronics. Most of my interactions with customers concern warranties, returns, troubleshooting, etc. I'm wondering if anyone here has worked in a German call center before and could tell me what sort of vocabulary and phrases I'll probably be using often.

Second question, and this one is kind of stupid: Although I've spent lots of time interacting with Germans, I've never done so as a customer service representative. Should I maybe tone down the super sweet and friendly tone I use with American customers?

Any insight would be much appreciated!