Lousy paint jobs and even worse preparation, poor plumbing using incorrect fittings and/or materials, rotten wiring by colour blind dyslexics, tiling over plasterboard in wet areas, filling an entire roof space with styrene offcuts to save a few bob, DIYers will try just about absolutely everything that you can imagine to save a quid, do it easily, do it cheap because they don't give a crap whether the poor bugger who buys their heap of &&&& dies from their styrene in a fire, has their family get electrocuted or if they are afloat in sewerage...... Even worse, the cretins don't seem to realise that in a lot of cases it could be their OWN family that cops it!
There are quite a few DIYers out there who go to great lengths to make sure that they do a good job of their homes, they are the ones who aren't afraid to spend a few bob on the best quality, correct materials, they are the ones who ask tradespeople how to do the job properly, not some flaming DIY nitwit who imagines he is an expert. They also are the ones who get the properly qualified people in to do the parts that they REALLY aren't equipped to do properly.
However, on this forum they seem to be outnumbered by the idiots who will tell some newchum that is OK to tile over old tiles, potential pyros doing their own electricals, use particle board intheir wet areas. There are some bloody good tradesmen on this forum and they give some bloody good advice too(NOTE: NOT INCLUDING AL!!!), but there are also too many morons who think they might have an inkling of an idea about a task so they advise poor old newchum to do absolute dumb schite to their homes....