Three years of financial statements, the payroll register, the manufacturer's dealership agreement and written confirmation that the manufacturer will accept new owners, plus the lease, the inventory list and the customer or service-contract book. Those documents are the E-2 case, not just due diligence.
The seller's records prove substantiality and non-marginality
A consular officer will want to know that the enterprise is real, operating and not marginal, and that the investment is substantial relative to its cost. The seller's financial statements establish revenue, margin and the value being paid for; the payroll register shows the eight employees whose jobs make the business more than a family livelihood; the dealership agreement shows the enterprise's right to sell and service the brand; and the manufacturer's consent shows that right survives the sale. The lease or title shows premises.
The inventory and equipment lists show what the purchase price buys. The couple should also obtain the seller's confirmation of any liens on inventory, because floor-plan financing that transfers with the business affects both risk and control. Assemble these before negotiating price, because the price must then be justified as fair in the application.
Keep the land-sale closing statement, the corporate resolution authorizing the distribution, the bank records of each transfer and the escrow agreement with them as the source-and-path file.