Remember letting agents are not really paying the bill,the landlord is,direct or through rent collection
If you do job as rent is due and you invoice just after rent paid to landlord,if not otherwise arranged, you are going to have to wait till the next months rent,so time processed,long wait,then you have problem,that if you do job and estate agents fees due from landlord,they come first,so you join the que,ect.ect,ect
On bigger jobs ,I like to talk to the land lord direct by phone or e mail to explain works ect,this also allows to raise payment and get acceptance of price in writting,also if I have not done a lot for agent,I would not do without contacting l/l
Agents will agree to something as they want things sorted out but have no real power to pay,if l/l rings and says he is only paying 80% of bill,thats all they can pay,then you find l/l in dubai
It is very important you know the system you are working in
But as said the longer you have to wait,within reason,the better,it keeps other smaller boys off your turf and allows you to add a premium but you have to keep on your toes
conditions on invoices are not going to do a lot,if you say you want payment within 4 weeks and they pay in 8 ,what are you going to do
imho