Hi the coating sealer is like a protective coat i have never used this as i feel it clogs the lashes and again your putting extra pressure on the extensions when you remove it. Yes you can retail it but like i say i don't use it so don't retail it. You can retail the mascara but again i've found clients put far too much on even when you tell them just to put it on the ends and when you come to take it off you can't get it off without pulling the extensions out.
I do use the thicker lashes but they are Hollywoods and again i have no problems so it's nothing to do with the lashes. Are you putting too much glue on and are you using Lash Bond glue?