pro tip for grilling burgers, learned it years ago:
when you are making the burger patties, add a tablespoon of apple sauce for every pound of meat
you won't taste it when it's cooked, and it keeps the burgers nice and juicy inside
Also, to keep it flat, make a thumb indentation in the center of the burger on one side.
I do something similar with added juiciness, since I tend to use very lean meats, even when cooking my own burgers (which is not recommended, but high fat meals send me for a tizzy).
I basically make my own burgers almost exclusively now since the toppings I like aren't at all common and I really don't white bread anymore, even on hamburger buns. No flavor, empty carbs = icky.