J Scott, thanks for clarifying the problem. It isn't that PMs are being dishonest or trying not to fulfill fiduciary duties. The problem is that compensation for most Property Managers is not in line with what is best for the Investor (just like J Scott's example with a buyers agent).
I think a one year tenant guarantee is nice, but doesn't solve the problem by itself (regular turnover that benefits the PM while hurting the Investor).
How about this structure:
Instead of 1 month placement fee: 50% placement fee
Monthly Management Fee is on the high side: 8%-11%
12 month Tenant Guarantee (no new placement fee if Tenant stays for less than 1 year).
To alleviate some loss of income from putting Rental in the MLS (typically agents like to see 50% of one month's rent), ask the Investor if they want the Property in the MLS and charge an additional fee to put in the MLS at their request. MLS is not totally necessary for rentals.