ok... I see where you're coming from.
The problem is, the existing business is just as unknown. For any business consideration I would start with these basic questions outside of the financial questions.
This is purely a starting point, and is by no means approaching a complete list.
Questions for them and for yourself:
AA) Why are you selling?
1) Have you chosen the best product available? Show me? What testing did you go through to determine this?
2) If mulitiple suppliers carry any of these products, have you negotiated the best price? Who is your contact there?
3) Is your pricing structure created for proper market positioning? Please explain.
4) Is the design and layout of your shop efficient? (good design will save you 1-2 employees per day or 15-40K per year. Show me.
5) Would you adopt their methodology? How do you know its the best way?
6) Are any employees involved? If so, you must fire them all and re-interview--they may not be suitable employees.
7) Do customers come based on quality of product and service OR do they come based on gimmicks (coupons, discounts, low price crap)?
8)Is their equipment equipment you would have chosen?
9) Has your equipment been professionally maintained and serviced?
--Do you have records/ maintenace logs to show this?
10) Is the color and lighting in the space correct to create a proper mood?
Was the lighting/design chosen based on solid reasoning?
11) What is the lease? Is it renegotiable? Is it even assumable? (Only wording in the lease plus the landlord can confirm this.)
Financial Questions.
1) What is percentage of monthly, yearly growth? Show me.
2) Business tax returns for past three years. P&L statement.
3) How did you determine your pricing?
4) What are your COGS?
5) What percentage you pay employees, and self-- does this match with tax returns?
6) What types of external marketing have you done? Show me examples.
Has this been successful? Can you quantify?
7)What types of internal marketing have you done? Show me examples. Has this been succesful? Can you quantify?
Etc., ...
All of these questions should be answerable. If anything wasn't answered, I would kill the deal immediately. There are no grey areas for me. Either it is a good business, in which all of these are basics for any decent business owner OR it is a bad business, they are bad owners, and have a broker just out for a commission. Any corresponding answers from different questions should match. Answers will show 1) Honesty/Dishonesty. Dishonesty is any exaggeration of aspect of the business.
2) Understanding of business. This goes hand and hand with honesty. A poor understanding of business will reflect throughout. Numbers sometimes lie. Success isn't determined solely by a good tax return and balance sheet. Additionally, the broker for whatever business you look at is a reflection of both the owner and the business. Good broker, no b.s. just the facts... good sign. The opposite is even more true.
Always remember you are in the 'driver's seat'.