How bad does an investment property need to be to warrant selling it?

If you sell a dud investment property, you may have to pay capital gain tax (CGT), selling costs and then stamp duty again when you reinvest… it can be a very expensive exercise! And if you have owned the property for a while, it is probably putting money in your pocket each month (i.e. more than covering its expenses – not costing you anything) and the CGT could be significant – even more reason to not sell it, right? This is what I would like to investigate in more detail. In particular, ho...