Cost for Additional Tenants or Renting to Married Couples

[Jessica F.]

What is the standard approach when renting to an unmarried vs married couple? My thought was that if it's an unmarried couple, they must individually qualify to be a tenant or else their name cannot go on the lease as opposed to a married couple where their combined income is treated as single income and therefore would only need to qualify together. (Side note: is it ok to ask the married couple to provide a copy of their marriage certificate as proof?)

When you are renting to a couple, whether they are married or not, what is the rule when raising rent? If rent is usually $700 per month, how much can you raise the rent for additional person such as a spouse, partner, or child? I read somewhere that you can increase rent by 10% but I don't know if that applies for Philly as well. 

Lastly, I have a clause in my lease that says if a person not listed on the lease is found to be occupying the residence as a long term guest that there will be a $100 fee charged for each month. I also specify that anyone who spends more than 15 days/nights at the residence per month or has "tenant privileges" (such as a key to the unit) is considered a long term guest and will incur the fee. Is there a rule for how much of a fee I can charge? I make the fee high to detract tenants from moving in any deadbeat friends/boyfriends, etc (I've learned from experience).

My rental is in Philadelphia so I am specifically looking for tips and info related to that market.