The Norrisnator - Business Summary 2
Know your costs. Always. All of them.
10% is a fair profit margin for the business, this is after cost, wages, materials services etc.
Profit can fully depend on risk, if you are taking a large risk in a job, it is entirely acceptable to ask for more money.
Client rank system, quite normal! Work with those who treat you well, if you can afford it, work exclusively with those clients.