Never trust what's being displayed. The display rate is always the same throughout the entire JB. But when you actually go and change, they'll give you a better rate. Unless the location is at a lousy location with only 1 single money changer there - they give lower lousy rates (eg Pandan City, City Square).
A good money changer in JB for example is right after the Shell Station with 3 or 4 money changers stores. And all displaying the same rates. But when you change, they'll give better rates (advice is change at least a hundred sing)
It has been this way since many years ago, unless you're a noob and take their display rates as it is.