In a way it's impossible to not use anything from the 'modern' period due to him being from the modern period. You could say that, the definition of, cheating, in this scenario could be limited to direct application of creations beyond the capabilities of that time period, such as the 'factory' or in other words mass production of goods of similar quality by use of manufacturing techniques which did not previous exist. Branding, or specifically, creating a local specialty in order to create a demand higher than available supply to increase prices isn't necessarily beyond the capabilities of that time period. It's the same idea as that the blacksmithing of tools at a location that close to an iron mine/mineral mine would be better than a location of a plains area, hence any tools branded as being from that mines location being 'better' than the ones made at the plains.
Now, how exactly is he going to take advantage of this, that's a different issue. Just because the idea's there, there's also a reason why it isn't exactly easy to become famous in any time period lol.