Well, now is a great time to sell that lake cabin.
But, the agents you have talked to, do they understand all the issues?
Is the septic good or is an upgrade in order.
Is there room for an upgraded system.
How about the well? Test it? Shock it? Purge it?
How close to the waters edge can you build a permanent structure?
How much does the water level change? It there a chance of flooding the house?
Are there restrictive covenants?
Can you upgrade the structure ow tear down and build new?
Is there a lake association and what kind of issues are enforced? (Yes asso. have the ability to allow or disallow issues and actions)
Ask the agents about these. They should know about them and if not, consider a different agent