Owner financed business purchase

I ran into a business being sold at 550k. It advertised owner financing . They are getting retired ( husband/wife) . Husband who started business started this IT services about 15 years ago . They owners are taking about 200k combined salary after paying the other 3 employees. Most customers are on fixed monthly agreements. It look like after paying themselves and the employees , they had a net profit of $100k in 2023 , but had a loss of 40k in 2022. Otherwise, 2024 look about the same as 2023 . I have own business in the same industry which works out of o take over . I am sure there are others in my industry that would want this deal . What are some fair options that I could offer with owner financing. One of the owners , is selling to stay around for a year . The business has about 20 commercial clients all of which are small business. So, relationship is important as if they jump ship after the sell , it would be a big problem. I think 550 k is two much but I don’t mind some cash upfront and percent of profits for some time . I want to be fair but want to protect myself . Your advice is appreciated. ( sent from mobile , forgive the mistakes )