Nothing wrong with the ones @finley appears to be obsessed about.
For those that are sold cut at the night markets it’s mainly a hygiene issue. The climate promotes microbiological growth, the equipment is not cleaned regularly and the vendors often either do not wear gloves or use the same gloves to handle money. You’ll be fine 90% of the time, but people do get sick from this and, while it’s a temporary problem, you wouldn’t want to spend 2 days within jumping distance of a toilet.
In general, Taiwanese fruits are awesome, but either buy them from a place with running water or get them at a fruit stand and peel/cut them yourself.