Two apartments of the same size, in the same community, built within a few years of each other, can carry service charges that differ by a factor of two. That is not an error and it is not always unfair. Here is what actually drives it.

The legitimate reasons

Amenity. A pool, a gym, a padel court, landscaped podium gardens and a staffed lobby all cost real money every year. A plain building with a lift and a cleaner costs far less to run and should be cheaper.
Whether chilled water is inside the charge. This single line moves the number more than anything else, and it makes naive comparisons between two buildings meaningless.
Building height and lift count. Tall towers cost more per unit to maintain: more lifts, more pumping, more facade to clean at height.
Age. An older building has real maintenance rather than theoretical maintenance. Sometimes the higher charge is simply honest.
Facade type. Full glazing needs cleaning and eventually resealing. Painted concrete does not.

The reasons that should worry you

No reserve fund. A low charge with nothing set aside is not a cheap building, it is a deferred bill. The next major repair arrives as a special levy, and you will pay it.
An inactive owners association. Where nobody scrutinises the budget, costs drift. Ask when the association last met and whether the accounts were questioned.
A charge that has jumped sharply, which usually means either deferred maintenance catching up or a management change. Ask which.
A developer managed building with no handover to owners. Worth understanding who is deciding what you pay.

How to compare two buildings properly

Put both on the same basis. Take the approved figure per square foot, add chilled water where it sits outside the charge, and then look at what each actually provides. A building that comes out higher and delivers a working pool, a maintained lobby and a funded reserve can easily be the better buy.

Then ask for two years of history rather than this year alone. The direction tells you more than the number.

We will pull the figures for a shortlist before you offer. How to look up any building explains where they come from.