Usually I am friendly .... offering frequent "good shots" when warranted. I am firm and clear when I think a call is in doubt or a if a rule has been violated, but generally sociable.
However, the only real attempt at gamesmanship I ever made was in a match against a far superior doubles team. I was overly complimentary and extremely chatty and friendly to our opponents. My partner later questioned me as to why I would do this and I was honest when I said I was trying to disarm them with kindness.
Unfortunately, like usual, the best team won ... but it was a really close match and I think my "gamesmanship" did end up helping to keep it close.
"You should be playing linebacker, not singles."