A conventional loan is a mortgage that is not guaranteed or insured by the US government. Conventional mortgages include construction loans, portfolio loans, and subprime loans. Conventional loans are the most common type of mortgage.

Fannie and Freddie follow the below criterion to evaluate mortgages they purchase:

They must meet the conforming loan limit which is evaluated every year
Loans with borrowers who have a minimum Credit Score
It meets the GSE guidelines in regards to Debt-to-Income ratios
Private Mortgage Insurance (PMI) is required for all loans where the borrower has less then 20% equity
Many more guideline
It is important to understand that neither Freddie Mac nor Fannie Mae service the loans they purchase.
Basically, even though these companies purchase loans from various lenders, it is the lender who retains the servicing – just a nice way of saying “we collect your payments.”