Tenant Screening - Background and Credit checks

[Tarcizio Goncalves]

HI everyone, 

This might sound like a dumb question but I am going to ask it anyways:

I found a potential tenant for my property. Its a mother and three kids. Two are in their early to mid-twenties and the other one just turned 18. Income and employment checks out as I already checked employment with their current employer. I am now asking for a background and credit check. Here is where I am a little confused:

Does everyone over the age of 18 needs a background and credit check or should I only focus on the mother? The 18 year old might not have a credit history yet. If everyone needs a credit and background check ($40 on average per person) what should I tell them if they complain that this is too much money? I would think that everyone needs a credit and background check but I also want to be reasonable and not have them walk away. They seem like good people from what I found so far. 

Thank you everyone as always

Tarcizio