I read it's best to get pre-approved before I start looking. 

I'm sending direct mail to a list of owners who have pre-foreclosures.

I make about $39K per year and was pre-approved for $170K loan.

I have clients that own 1 to 5 vacation rentals here on Mau i and once you hit that threshold of 5 you may be put into a commercial status (5+ units), so qualifying can be a bit more difficult, looking at such things as:What has that person owned and what has been their management experience collecting rent and managing propertiesThe borrower's credit score, income and personal and business tax returns will be considered along with two years' operating statements and a current rent roll for the property.Also important are property metrics, such as: Net operating income: The annual income, minus expenses that a property generates from its operationsDebt service coverage: Measure of cash flow relative to debt payment obligationsLoan-to-value (LTV) ratio: A measure of the loan amount relative to the value of the propertyThe property has to service its debt at a comfortable marginOf course each lender can be a bit different, so it's good to shop around if needed.I hope that helps.BTW - what do you consider big money?  

Agree with @John Anderson , and suggest getting a pre-approval letter from a lender for proof of funds (for amount you think the house is worth) to show your seriousness. 

Hey Mark Douglas congratulations on your second property and keeping the ball rolling.

You must also be able to prove the ability to purchase the property with cash or pre-approved financing.

I've submitted mine and my wife's information to two lenders (one mortgage broker, one through B&W) and we've been waiting on replies from both for pre-approval for going on two weeks.

Screen, screen, screen and don't ever compromise just to get the rent checks rolling in. 

If you are going to finance deals have a pre-approval letter ready when you make an offer.