Ad reach per purchase

Hello BHW

I'm currently doing an ad campaign in facebook, it's been active for about 6 hours. I have two questions regarding the results so far.

My ad relevance score started at a 9 then about 5 hours later dropped down to a 7, which is kind of confusing to me. Any reasons that might have happened?

Also, in your experience, what reach on average you get until you make your first sale through the ad campaign?

Thanks