Am i the only one who feels like giving money as tip, esp to professionals, feels a bit gauche?
No, you are not. You are absolutely correct.
I don't have most of the services listed here. If I had a maid to clean my apartment regularly, I would tip her the value of one cleaning, which seems to be the accepted amount, assuming that I was happy with the service.
I will not tip the garbageman.
Mailmen are allowed to accept non-cash gifts up to $20 in value ($50 total per year from one person). They are not allowed to accept cash. Trying to give them cash puts them in an awkward position of having to either refuse a kind gesture or accept it and risk their job.
Tipping teachers with cash seems to be terribly fraught with ethical problems. Contributing anonymously to a PTA or classroom fund or sending a nice homemade cake or something would seem to be a better approach, and this really should be done at the end of the year after grades have been submitted.