I recently had a chance to by a fixer upper and noticed that the dry wall joints had been badly taped and could be seen through the paint and/or falling off all together. What is the best way to handle this?

Peal all the loose tape off and retape with fiberglass mesh tape except for any corners then use paper tape. You can't spackle over loose paper tape it will never work.
In areas where the tape isn't loose but can be seen through the paint, they probably just taped and painted w/o any finish coats. There you can just spackle over the tape in those areas.

I agree completely.

Terrible job was done in my wife's house before I married and moved in.

Pulled off the loose and retaped. Where it was showing but not loose I covered with mud and sanded. All worked out fine.

I was hoping that would be all I needed to do, a local contractor suggested retaping the entire house, and I wasn't to thrilled with that.