Soupdawg,
I love those books whereby the owner is retiring. Typically, for the seller, it is detrimental taxwise to receive the entire value in upfront dollars. Therefore, you can structure a payout that works for him during retirement and could allow you a book that is immediately accretive to your bottom line.
Non-standard books vary depending upon the carrier, rates of commisson being paid, and historical retention. Obviously, the worst case scenario non-std. book of business for the "seller" would be valued at 50%-75% of annual commissions.
As stated by Cathy, standard and preferred lines should bring an increased price depending upon retention and the lines of business, agency length of time in business, whether you are assuming his location or just moving the book, taking employees or not, assuming any ongoing liabilities such as phones, copies, or other leases, etc. etc.
Lastly the same idea applies to commercial books.
Personally, I would perform an extensive due diligence on every book individually utilizing all carrier reports available, paper and online. Request written authority to verbally speak to any company dept. regarding his books.
Be sure the producer agreement clauses requiring the carrier's notification and agreement of your purchase are satisfied as well.
Then, structure the purchase and potentially increase the value by extending the payout time on the best retention books. The I.R.S. requires that you pay interest on any outstanding balance but that can be "backed" into.
Finally, one more important point, be sure to contact your CPA for the optimal allocation of the purchase price ( assuming an asset only purchase) such as allocating the proper percentage of the purchase price to the customer list, book of business, F&F, Goodwill and Covenant Not to Compete.
As the buyer, you gain significant tax advantages via differing lengths of time to depreciate each

asset versus just allocating the entire price to the book of business.
This has been very helpful to me in past acquisitions. Your CPA should know what is best for your corporate structure.
Hope this helps.
Regards,
Hutchman