I think you have to factor in weather, amount of labor involved, politeness, completion of work, etc. If they are rude, no tip. Otherwise, depending upon my assessment of the job determines the tip. Had a delivery of furniture a month ago, crew left debris and didn't have the mounting brackets for a hutch they delivered(crew should check when loading items)- no tip. Oven delivered on time, and checked over by delivery crew - $3.00 tip each. Install done by seperate crew, removed old oven and took time to balance wall unit - $5.00 tip each.