3 year old windows should not need tweaking.
Cheap hinges might have been used in the installation. Generally, the only time I find a window (new) that needs "tweaking" is in an apartment where a tenant has run a coax cable between the frame and window causing the window to be knocked offline. In this case the hinges need replacing
On the otherhand, I have come accross cases where window installers delivered the frames and windows seperately to housing developments. This has resulted in the windows being installed into the wrong frames. While they might look ok, and the gap might only be a mm or 2, it is enough to let in outside air. There is not much can be done in this case. (Just came accross this in an estate in Balbriggan). Packers can be used to try to realign the window in the frame.
When you are looking for a price, look for a day rate as opposed to a price per window, otherwise you will be screwed!
Also remember, it takes 2 men to safely remove an upstairs wndow, (It can be done by 1 but its risky).
Sorry if I have not answered you question, but I have given you the information you will need to know when dealing with repair men!
For a recommendation of anyone (which I would be reluctant to do) I need to know your location.