How to know the size is right? What you need to know after buying inline skates

The short answer: Commit to skating them in house

Never put on a pair of skates and then, while not even tightening them, decide that it is not your size.

When you get new skates, first put in the laces before you put them on. Skates have allot of padding in the back that pushes the foot forward and you need the closure system to push your foot back in to this padding.

Close the buckle, laces and straps as tight as possible. Then, make sure your ankle joint is as close to a 45 degree position. This means bending your knees a bit and press your shin against the front of the skate. This is the skating position and this is the position you should use to consider the size. Do not judge the size in any other stance.
Skate around the house a bit and see how the control is.

It should feel very tight overall, but not have a specific pressure point.

A good way get some indication of how this skate works with your foot is to take out the liner and try the shell without the liner. Never put on the liner without the hardboot shell. You need the shell, laces and buckle to push your feet back in the liner. A liner in your size will always feel too tight when tried on without the rest of the skate. Instead put your foot in the shell, shove it to the front so that your toes slightly touch and then feel how many fingers you can put in the back behind your heel. It should be more than 1, but not more than 2 fingers. If its less then 1 finger you will either need a way smaller liner (not smaller size but with less padding) in this shell, or you would need a bigger skate. If you have more than 2 fingers of room in your skate, then your skates are most likely to big.