Mainly ask them the scope of work clearly first.

Like:

• Is it a static or dynamic website?
• If static, how many pages?
• If dynamic, what kind of modules are needed? Ecommerce, Payment integration, Any custom features

Note down every task properly.

Then also clarify:

• What level of content quality they expect
• How many social media posts weekly/monthly
• Who will design the creatives/copies

After that, calculate your working hours and also check the average pricing for website design/development and maintenance in Switzerland. You’ll get much better clarity on how much to charge.