There is really no way to get a good return when clients wear heavy makeup and eyeliner. Removal is damaging to the EE and will cause them to fall out. There is no way around it. The client is choosing to wear the heavy makeup so unless she is taking great care of removing the makeup with out disturbing the EEs they will fall out.

If customers stop using revitalash or other eyelash growing serums.. their lashes will go back to the size they start. It is definitely OK for clients to use products like these because the more lashes they have the more you can apply. The more you apply the better and lusher the eyelashes.... The more they will love. Eyelash growing serums are a Extension artist best friend. I always encourage them to use it as directed, not to go overboard.

As for retail. you can sell sealer, EE wash, liner, heated curler. Anything to deal with lashes. Tons of product out there. You just gotta figure out what brand you wanna sell..