It's common yeah.
One thing I hate though is when a game extends for 40 minutes when the outcome of a loss is known. Like 100% a loss unless enemy team feeds kills intentionally. I've noticed this happens all too often and it just sucks to be held in a match that's an obvious unwinnable condition (think 0/6 top laner 0/4 mid laner 2/5 jg and 3/5 adc). For some reason they don't surrender until enemy is attacking inhib and personally I'd much rather of just surrendered at 15 than be forced to play a match our team has absolutely no chance on.
Sorry, that was sortve a branched off rant. But yeah, afking and trolling is pretty rough, and also annoying when there still is potential to turn the tables. I still play even when they aren't despite really not wanting to.