Can you not only get a gram?

I’ve recently started smoking Mary J and the thing about me is I don’t like getting bumped when getting bud so what I do is I ask for a G first but for some reason they never wanna just give a G they’d rather not give it all and always true getting me to get a 3.5 but me being in sales I never want to budge as I’ll feel like I’ll be hustled. Is it an unspoken rule not to buy a gram or something? Or am I just talking to the wrong people