Re: price
sorry the motor is sight un seen. just what a 150 hp. is going for
There's simply not enough information in your posts to give you a number. A lot depends on condition. Get the model number from the seller. Is the engine on a boat? If so, along with compression testing, etc., try to get an on-the-water demo.
Whatever you do, don't buy any outboard that new without running compression and spark tests and a thorough examination. Also, all controls should come with the engine. It's expensive to buy them again.
You cannot rely on what the seller says. That much is certain.
Then, start hunting for equivalent engines that have been sold in your area.