Turns turtle, that's a stretch. Modifications like the ones seen in this boat are done all the time and boats are not flipping over right and left. But all you'd have to do is request to see the stability test results done after the modifications. If there is not one require one be done prior to purchase.
Capt....With Respect......
No one expects ferry's to turn over suddenly on a calm day either. But it happens and hundreds of kids drown. The part that frustrates me is that this is foreseeable and preventable, yet we keep getting it wrong.
The typical US powerboat of 50-60' length is 17'-18' wide and of hard-chined form. If you have a 50-60 footer with 17' beam and hard chines, I have no problem with adding a permanent hard top on the flying bridge. Just make it as light as possible (foam cored with light plastic windows). I will seriously question also adding a big hard-bottom inflatable, and another dinghy, and a crane, and a sun-deck top, and a mast and antennas as well!
But this Gulfstar is only 15' wide, a round-bottomed sailboat form, and originally relied on fuel for stability! Hopefully anyone can see that once its burnt the fuel no longer adds to stability.
The hard-chined form is very stable at low heel angles, which is why people like it. You step aboard and the boat heels a bit but corrects quickly back upright and stops. Very reassuring but can be tiring at sea.. The round bottomed form is not as stable at low angles, you step aboard and she may continue to roll down underfoot, then roll back beyond upright, then back, and slowly damp out the rolling. Not so reassuring......but more comfortable at sea.
The typical hard chined boat may run out of stability at 60-70 degrees heel. This is rarely a problem because the hard chine form snaps her back upright at low heel angles. But the round bottomed form does not, she just keeps on heeling. And with the high center of gravity the modified Gulfstar may run out of stability at 50 or so degrees heel. That is a scary thought.