Unlike some sports - football, rugby, boxing, for example - a big lead in a darts match does not allow a player to sit back and see out the game.
There's no equivalent of taking the ball into the corner to waste a bit of time in darts, you've got to hit that winning double to get over the line, and for some players a winning double can prove problematic.
When playing with such fine margins, tension can play a big part, so make a note - mentally or physically - of players who become a little nervy when the winning line approaches, and be prepared to lay them at short prices.
Equally, some players can be naturally slow starters in matches, before picking up the pace when they get into a rhythm. If you fancy a player to win a match, but know he can be a slow starter then you could get a much bigger pricebetting In-Play than you would pre-match.