He-he... That sounds like a great business plan. Use for example Oanda's API to get the fx-rates for free, and sell it to people that doesn't know any better. If they can trick anyone, it is a 100 % profit margin business.....
Oanda api is $400 a month. https://www.oanda.com/foreign-exchange-data-services/en/exchange-rates-api/api-pricing/
Just open a free trading account and use their free API. They even have code examples on their developer pages about how you can get tick by tick trades for free. You do not even have to code. Just use their code, and off you go...
You can certainly do that [referring to your proposal of reselling data] but if Oanda finds out about it I assume they will stop it. The intent is that you're a trading customer after all.