Guys don't be donkeys here...
If the dealer had drained the oil and not added new one, that engine wouldn't have lasted more than 2-3 km before completely seizing.
If maintenance had been neglected by the owner, and the engine had be running low on oil, the damage was already done. It made no difference whether the dealer topped it up on Friday.
If the engine seized by Monday, it means oil starvation damage by Friday was already too severe...
- Scored cylinders.
- Scored cams.
- Scored bearings (I suspect this is what happened, due to oil starvation the bearings wore over time till one of them was too thin and either broke or spun seizing the engine).
I know looking for blame on others, or saying Thais bad is the easy way out. But the only one to be blamed here is the owner. The dealer did nothing wrong. Even if they had added oil on Friday, that engine was mortally damaged.