PROS: (1) probably will cost you less, in terms of loan charges at the time of closing. (2) may POSSIBLY allow for more wiggle room to negotiate the interest rate, length of the loan, and similar terms; (3) may possibly allow you to buy properties, or borrow more money than conventional lenders might be willing to lend on

CONS: (1) few sellers are willing / able to give such financing; (2) few sellers are equipped to service loans as efficiently as conventional lenders - it will be harder to get a payoff statement and / or release of the mortgage when you are ready to repay the loan in full; (3) greater risk of disputes about the accounting / allocation of payments to principal, interest, escrows, or other costs (4) risk of problems if / when the seller-lender dies or moves out of state or sells the paper to a third party; (5) risk of seller not reporting interest payments properly to IRS or state department of revenue

It is alway more advantageous to use owner financiaing if you have a Seller willing to do so.
You will need to give the Seller a down payment. Or, you can agree to a lease purchase where 10%, 20% or more of your monthly rental will go toward the down payment amount. Once you have reached the initial down payment figure with the Sellers, you can then purchase the property with owner financing or with a mortgage from a financial insitution. It is always better to utilize ower financing.