I'm all for agents too! They'll do anything they can to sell your hide. If you tell them your terms and conditions of employment, they'll do their very best to meet your requirements. Some can even arrange Z visas for you if you don't have at least a BA. God knows how, but they can! It seems they can work magic.
Heed not their critics. Most of them are degree snobs who revell in feeling superior to those foreign teachers who haven't been to uni.
Unfortunately though, many agents are cheats and liers. So, take great care which one you choose! Good ones do exist, allbeit just a few.