Selling or reselling products that you can make or buy for 10% of the sale price is the way to go. My favorite is items that you can buy for $10 or less and sell for $100 or less. My businesses like that have a 90% gross margin.
The only thing better than that is information based products such as what Tai Lopez sells. The cost of those “courses” is near $0 and when he sells them for $67 then about $1 is cost for the servers and the rest is all profit. Of course, you have to invest a lot into marketing those information and education based products too. Tai spends over $2M a month on advertising.