Having left full time teaching for a job in the NHS while I train for a specialist teaching role, I signed up for two agencies. One (a big, national one used by the neighbouring county) has only been in touch now for the first time since last July - and they want me to re-register and provide yet more references! The other is used by the county I live in and they offer me occasional work but it's usually on the days I've told them I already work or TA work because they have a TA with the same name registered!
I've started using my own contacts to put the feelers out for supply and am now fully booked. I'm declining to work for less than UPS3 as I want to protect my salary for when I qualify in my specialist role.
I think it's time to cut the dead wood with useless supply agencies who expect us to work for the bare minimum. Just intending to encourage people in a similar position really, but I think if we supply teachers use our own networks and demand what we're worth, supply agencies won't be so able to call the shots re pay.