This happened to me a few weeks ago in a straight pool league match. There is no specific league night so we just scheduled the match on our own time and this was first time I've ever seen/met my opponent. It was just the two of us without any league director or ref.
He was a nice and friendly guy throughout the majority of our match. However, he became very frustrated with himself when he missed his last shot and left the table wide open for me run the last 12 balls and win. He said "there you go, run them out..." and then he proceeded to unscrew his cue and start putting his equipment away. I paused for a second to see if he was actually conceding or if he expected me to run the balls. It was clear that he expected me to runout to earn the win.
I'm sure I could have argued that by unscrewing his cue he conceded the match already. That would have been easy but it would have pissed him off and ruined the small friendly relationship that we had developed over the past few hours of play. It also may have cost me action in the future.
So I didn't say anything about it. I just ignored him and ran the balls out. It wasn't a hard run out and it's not like we were playing for huge bankrolls. Plus his sharking was kind of a compliment in a way, by acknowledging that he knows the run out is easy for me.
In my opinion, it typically isn't worth the energy to argue with people who are actively sharking you. You'll play much better if you keep quiet and pretend that you don't notice or care. My philosophy is that once you become agitated or upset, you've already been successfully sharked.
Every situation is different but generally speaking, if you keep quiet and focus on running out you'll have the most success. Just remember, once they decide to start sharking, they've already admitted to themselves that they can't win. So just keep playing your game and you'll bury them in no time. Then you can smile and shake their hand with a shit-eating grin while they are beating themselves up inside.
On a similar note, whenever I gamble, I always expect to get screwed a few times per match. So I match up expecting to get screwed on a few close calls. Then when the argumentative situations arise, I just give my opponent the benefit of the doubt and move on. This keeps me from getting upset and keeps the match flowing, even though I'm getting screwed. It's all figured in at the start, so I'm not surprised when it comes up
