Expense Ratios

In reading the MHPS course materials, I learn that I should be assuming about a 30% Expense ratio when doing my initial analysis on parks I want to purchase.

This can be tightened up once we go to contract and I have a chance to review actual expenses. However, I am seeing some parks where the seller is claiming

as low as 20% (for parks with no POHs). If I immediately ignore this and apply a 30% expense ratio, I find that my valuation is way too low for the seller, who claims

that his expenses are accurate.

My question is, isn’t it feasible that some sellers could have raised rents at a greater percentage to rising expenses and achieved a 20% expense ratio over time?

Isn’t this exactly what the MHPS course teaches us to do (10 CAP to 20 CAP)? Would appreciate feedback before I dismiss deals that may be legit.