How can I flirt with and know if my singing teacher likes me?

So I have been having singing lessons on Skype with my brothers next door neighbour, we are both of similar ages and I really like him, we get on very well and have a good laugh and joke together as well as talking about our families etc I just don't know how to flirt appropriately during the lesson and help move the relationship from professional to something more personal. Any advice or any signs to look for from him would be really helpful!
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I would like to add the singing lessons are not attached to a school or any educational establishment he is self employed and 25 and I am 30 he is just doing the lesson for extra money during covid 19 and living at home with his family currently so no laws are being broken etc
How can I flirt with and know if my singing teacher likes me?
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