Boats are holes in the water into which owners pour bad ideas. DIY repairs are often more dangerous than the original defect.
1. The "Paint Over Rust" Special
The Sign: Fresh, glossy white paint on an engine mount that has pitted, bubbling texture underneath.
The Truth: The owner spray-painted over heavy corrosion to sell the boat. Poke it with a screwdriver. It will likely crumble.
2. Mismatched Fasteners
The Sign: A deck cleat held down by 3 Phillips screws and 1 slot-head screw.
The Truth: This cleat was ripped out and re-bedded hastily. Check the backing plate. It's probably undersized or missing.
3. Household Wiring
The Sign: Solid copper wire (Romex) used for AC systems.
The Truth: Solid wire work-hardens and breaks from vibration. Marine wire MUST be stranded and tinned.
4. The "Goop" Solution
The Sign: Massive amounts of silicone sealant around a window or fitting.
The Truth: They couldn't stop the leak, so they just kept adding goop. The core around that window is almost certainly wet.
Conclusion
If a repair looks unprofessional on the surface, it is dangerous underneath. Trust your gut. If it looks wrong, it is wrong.