You might find more interesting data on women being paid more, in the entertainment industry, as the economics of women being more attractive creates specific incentives for certain targets markets. Likewise you may find that specific cafes have branding policies which are biased towards hiring either attractive men, OR women, but (often not) both at the same time. I would encourage you to (visit many cafes), to familiarise yourself with the market. Let me know if you have any observations to discuss from your study. :)
Pop by during busy hours, and observe for 1-2 hours per cafe, the interactions between staff and customers of (any) gender. Look for patterns and see if you discover anything, at any particular cafe. It can be quite amusing.
You can look through the Instagram accounts of each cafe also. That will save you some time.
Gender Bias, in F&B Compensation
So a candidate for F&B operations made an comment about men being paid more than women, in general. I thought that was interesting, and said something along the lines of:
tags: coffee work