Windows in Las Vegas take ultraviolet light, grit, and a west sun that loads a room faster than many cooling systems recover. Vinyl chalks. Seals fail and leave a permanent fog. Aluminum single panes in older houses are still a hot plate by late afternoon. Tracks fill with blown sand, then the one hard rain of the season pours through a gap the dry months hid. Stucco cracks at the corners of openings because the wall itself is moving with heat. That is a different complaint from a Tucson monsoon sill and a different one from a Freeze-thaw Front Range frame.
Say what you see. Fog, a soft sill, a lock that will not catch, or heat you feel from across the room. Count the openings and name the direction. A west slider in the living room may be the whole project. A north bath window may only need hardware. Older downtown houses and newer tract houses do not share frame sizes, so say which era you think you have without inventing a model name. If the frame is soft, an insert that leaves it in place will leak again.
Ask whether the job is an insert or a full-frame replacement that opens the stucco and ties flashing to the weather barrier. Ask who patches stucco and drywall. Ask how the sill sheds water so a cloudburst does not sit in the track. Ask what fills the gap around the frame, because wind and grit will find an empty one. Do not let the call drift into a promise about the power bill. The local issue is durability and afternoon heat on the glass you face.
Bring the count, the exposures, and whether sand is pouring through on windy days. That last detail is a Las Vegas detail. Call the number on this page.