Uninvited photographers hurt everyone!
Many events have "Sponsor" or Invited Event Photographrs - and many have photographers just show up and think they are entitled to shoot and sell photos without checking with organizers.
Not all events will have sponsor photographers, so how will you know? Simple, if you are at a dog event, there will be a check in area, or a secretary or chairperson - just ask them. They will let you know if there is a sponsor photographer for that event and who they are.
Most events are simply not large enough to support multiple companies, this is just one reason for having event photographers. It is to everyone's benefit to have established, professional photographer have the exclusive to shoot your event.
Not having a sponsor photographer does not mean the photographers there won't capture good images, but there is less control over quality when anyone can show up and shoot. This does not mean that a poacher doesn't take good photos, but by purchasing from poachers, photographers who have not asked for permission to sell at an event, or have a license or vendor permit, they will run off professionals by selling a sub-quality product at a lower price to get you to buy their photo. This will hurt everyone in the end.Back to everything you need to know about purchasing digital photography.