It's tough dealing with "mom & pop" sellers - don't expect to get great records. They should be able to provide a crude rent roll and provide utility expenses. You can ask about the taxes/insurance but you should just pull the tax expenses from the city/county and get an insurance quote yourself. Easy enough. Look online and talk to brokers to determine the market rents. Make sure that you have a broker on your side, unless there's a reason not to.
Once you have those, you should be putting together your own underwriting based on the in-place cash flows, as well as your stabilized proforma @ market rents, your estimated RET upon the sale, and your insurance quote.
Once you feel comfortable with your analysis, you can make an offer via and LOI (letter of intent), and make the PSA contingent upon receipt of all required due diligence if not yet received. At that point, You'll want to make sure that you at least have copies of the utility bills and the leases, to verify the rents at the property.
Again, it's tough trying to get good info on these small deals, especially if they don't think you are serious. You need to come with own analysis, get comfortable, make an offer, and then make the PSA contingent upon getting the rest of the due diligence.