Is it permissible to work as an intermediary between a website that provides services for a fee and other clients, by purchasing the service at one price and then selling it at a higher price without either party knowing that I am an intermediary?

It is permissible for a contractor undertaking a permissible task to delegate it to another for a lower wage, provided that the contractor was not stipulated to perform the work himself, and that the interest of the one who hired the contractor is not compromised. Working on building websites is permissible, provided they are free from forbidden content. Promoting advertisements on websites by attracting real visitors and genuine "likes" is permissible. However, placing unreal "likes" or deceiving the advertiser is forbidden, as it falls under the prohibited deception.