Seeing the date of this being over a year ago, it may not be relevant anymore, but if so, or atleast for informational purposes, here's some info that related to a shop my parents purchased in 2009.
My parents have also been pretty good business people, my dad a financial director and owner of manufacturing company and my mum in sales. In 2009 a family friend was selling their sweet shop in my local town and my parents were interested as my mum looked to take a leave from sales and a little sweet shop sounded good.
At that time, the lease was up for renewal so having been dealing with leases for x number of years, my dad struck a deal for a 10 year lease but had a clause in the lease contract that it would be reviewed in years 2, 5 and 8 and if the business wasn't making a certain amount of profit the lease could be cancelled, while this was obviously for my parents benefit, knowing the landlord would want something in place, similar to what you've said about possibly wanting an increase, my dad had thought of this already and suggested something along the lines of a 3-5% rent increase based on the profit.
Because my dad had thought about everything straight from the first instance when dealing with the landlord, the landlord was very approachable and went for this this and I think the only concern he requested was that he wanted suitable notice, understandably, if it was likely this would be triggered but knowing the business had been there for however many years already, he knew it was unlucky to be triggered.
Anyway, 6 years later and my parents have tripled the income of the shop and my mum is now looking to retire at some point this year.
