Surface type is one of the biggest factors, porous materials like unsealed brick generally take more time and product to fully clear than smoother surfaces like painted render or metal, which directly affects labour time on site.
The size and age of the graffiti also matters, larger coverage naturally takes longer, and paint that's had time to properly cure into the surface is more resistant to removal than a fresh tag treated within a day or two of appearing.
Access and location play a role too, ground-level surfaces are straightforward, while anything requiring height access equipment or work near active infrastructure adds complexity and time. A fixed quote after assessing these factors up front is the most reliable way to know actual cost before committing to the job.
