All for trying them on, however, some online places have a foam fitting system or will take drawings and dimensions. I have very wide feet, and explained this to everglides. Bought my skates there and was asked if i wanted blades fitting before sending, if they were not fitted I could send them back. Although the lower end riedells only come in one width the top ones come in up to 5, so it's crucial you give the right information if your not trying them on.
It's always a risk buying on-line, however sadly theres hundreds of people up and down the country who have bought ill fitting skates in skate shops. Either due to unqualified staff, or just buying the skates they want or can afford rather than the right ones for them.