What’s the best way to measure NPS in the service industry without bias?

I’ve been helping a client in the service industry improve their customer experience, and they asked me to implement Net Promoter Score (NPS) tracking. The challenge is figuring out how to collect this data in a way that feels natural and doesn’t pressure the customer.

We’re debating between sending a quick SMS after service, using email follow-ups, or integrating a small popup into the booking platform. But I’m also wondering how timing affects the score. For example, if we ask too soon or too late, the results might not reflect the true sentiment.

Also, how do you deal with internal pressure to only collect "positive" scores? I want to keep the feedback honest and usable, not just for show.

Would love to hear how others are doing this effectively without skewing the results