I agree with Dieselsmom, holding the treat just above their head and back a little will put them in a sit every time. Getting them to hold it just takes patience and repetition and lots of praise. Personally, I think that praise is a really important part of training. You don't always have a treat in your pocket when you need your dog to obey a command, and praise can be an excellent reward for them as well. Good luck with your training and WTG Merlin!!!