First and foremost, I'm not necessarily doing this for money. This is my hobby, this is what gives me joy.
I can relate to this. When I'm competing at an agility trial, I always take my camera along, and between my own events I take pics of other competitors. Sometimes I offer to sell them, mostly I don't. But it's fun either way. In my own case I've temporarily given up on photographing indoor agility. None of the professionals in our area will come to an indoor trial, and I understand why. It's really, really hard to get saleable shots without some kind of additional lighting, and there just isn't enough money to be made off agility people to warrant the investment in time and equipment, at least around here.
If I were you, I'd rent a fast lens and try out your venue. From the video, it doesn't look too bad - much better than anything we compete in around here. You may have to process out the colour cast from the fluorescent lighting, but it might be worth the effort.
Looking at your outdoor samples, if I can make a suggestion it would be to concentrate more on the close-up shots like the one of the white dog, and on those that include the handler as well (e.g. the one on the dog walk, with the handler alongside). Most of the others wouldn't be saleable. Some of them also look a bit under-exposed and out of focus. You might want to try bringing the exposure up a bit. Also, when photographing black dogs, you might try purposely over-exposing the shot to bring out the detail of the dog (using exposure compensation). This will blow out the background a bit, but at least you're going to be able to see your subject properly.
Have fun and good luck!
