I recently purchased a Grand Banks 36 Classic. With almost all brokers, your offer to buy will be contingent on a "satisfactory" marine condition and value survey as well as a sea trial. Buying insurance without a current condition survey is possible but very difficult--so consider a survey as mandatory. Bolz Marine Survey is Camdenton MO looks to be quite experienced--perhaps not with Grand Banks, but certainly qualified. So really, your financial risk is the cost of the survey. (Probably in the $600 to $1000 range.) If they find something unacceptable to you--you simply walk away. Or, if you want, you can negotiate repairs or changes in price.
If you like the boat, making an offer makes sense. Follow the surveyor around and that is when you get a chance to determine the condition and needed repairs.
Most brokers are a little reluctant to "commision" a boat that is winterized, just so you can hear the engine and generator run. But, in order to do the survey the boat will have to be "commissioned" ready to run for the survey and sea trial. If you can convince them that you are a serious buyer and not a tire kicker, and are willing to pay the cost of "un-winterizing", so that you can evaluate the engines, they might be willing.
$50,000 is a pretty good price. (Brokers very often build in 10% for bargaining-so do not be afraid to offer much less than the asking price.) Cat 3208 engines are good engines if properly maintained and operated. But be aware, other than loud banging noises, low power, excessive smoke, or excessive blowby it is difficult to determine an engine's internal condition without a history of oil analysis. So always assume that there is some risk of an old boat needing engine repairs----factor that into the price. (The engines on this boat should have more than 1000 hours of life still in them--maybe considerably more. There are many 3208's still running strong with 5000+ hours.)
Often, these boats are used as much as a weekend "condo" as for voyaging. The Grand Banks interiors are quality. The hulls are also known for quality. So, potential buyers may be people that like to spend time at the lake as well as those that actually enjoy traveling long distances in the boat.
Be aware that old boats are like old motor homes---even with good engines, there will be lots of work to be done----if you are not a DIY mechanic, cost of repairs should be considered, and if you are a DIY person, be aware that you will be spending lots of time taking care of the boat---be sure you enjoy that or selling your boat will be a happier day than the one when you bought it.