Interested in thoughts on how to treat customer deposit liabilities in an acquisition.

Target tends to run negative net working capital due to sizable advance customer deposits. These deposits are paid to reserve the provision of the company's services at a future date. Balance could run as high as 50% of the purchase price at close. NWC excluding cash has been relatively consistent over time. NWC including cash has fluctuated much more dramatically based on the amount of cash on the seller's books. Cash as a % of customer deposits as been as low as 25% and as high as 150%, most recently hovering around 100%.
Currently I'm treating this account as debt (essentially a loan from future customers), requiring that the debt be extinguished at close and excluding this account from the NWC peg process. Obviously I don't want the seller to go and refund these deposits, so the way to effect this would be having him leave an equal amount of cash in the business at close (preferable) or through a revision to the purchase price.

However, I'd like to be sure that I'm making a market ask. At some point his outside accountant will have eyes on this so I'd like to know in advance where the common ground is likely to be. Thoughts and advice from this community are welcome!