you are asking the wrong person
I'll tell you.
There are markets for doubles but rarely usually for SF/F in Masters and GS. V-bettors on mtf show no interest in doubles matches and even when we have interesting encounters there are very few bets on them that's why v-bookie managers don't create markets for doubles.
I would like to see doubles vBets too. At least for SF / F, like you said. I didn't see any of them in Toronto Masters though. We can have this when top teams are in the fight. Thanks for answering.