the merc 150 4 stroke is all of 12kg lighter so I would be amazed if this comes into your thinking, it has less warranty, is has sold a insignificant percentage of commercial engines with YAM and Honda having the most.
There is no corrosion issues so please think why someone would post such rubbish.
so how would I move forward if I was you .....
If you can try and get an independent trial i.e. ask the dealers to take you out for a quick spin and make your own mind up. Obviously I would pick a top 3 and different dealers to take you out for each different make.
I would also add that this is a great way of at least starting to get to know them as this will be far more important if something does go wrong than choosing between the different manufactures.
look at New Merc 100HP - Alarm sounding, loss of power, revs limited- World Sea Fishing Forums | Sea Angling and Sea Fishing Online | Fishing Reports
The fact that this was a merc is irrelevant there are bad Honda, Yam dealers as well!
Some dealers will also give better trade in prices than other, and some will even given you a few prices on what your new engine will be worth in x years i.e. we would give you x for it after 5 years with 300-400 hours or y if it has done 4-6 hundred hours.
This will also help you work out how much the different makes will cost you over the years you plan to keep it.
Hope this helps and please before you rule anything out give it a try.