Qualifying a cash buyer for viewing a property

Can anybody share with me some of the things that they ask of their cash buyers before walking them through any of their wholesale deals? I don't want to scare the seller by having 10-15 tire kickers walk through his house, so I'd like to narrow it down to a few buyers walking through the house. What's a typical number of people that you'll show the house to? Do you perform multiple showings? The house is currently occupied by a tenant. I know that I need to ask for proof of funds, but in what form? A printout of their bank statement? What else should I ask for?

I want to be completely transparent and honest with the seller, so I planned on telling him that I partner with other investors and will need to walk a few of them through the property for their evaluations.

Thanks for any help that you folks can give me!