In my experience at previous employment there were a lot of chancers in technical contracting for Java and front-end dev in London.
They all interview well, but when on the ground and asked to do stuff they are usually found out to be useless fairly quickly.
The "one weird trick companies dont want you to know!" is that it takes about a week or two for people to fully appreciate the contractor is useless and needs to be sacked, by which point they've made £500/day over a week or two which is £2500-5000 for half a month's effort which for a majority of people in London is a pretty tidy sum.
My lesson learnt from this is dont just quiz people in a face-to-face interview, but get them to do something in the interview.
They all interview well, but when on the ground and asked to do stuff they are usually found out to be useless fairly quickly.
The "one weird trick companies dont want you to know!" is that it takes about a week or two for people to fully appreciate the contractor is useless and needs to be sacked, by which point they've made £500/day over a week or two which is £2500-5000 for half a month's effort which for a majority of people in London is a pretty tidy sum.
My lesson learnt from this is dont just quiz people in a face-to-face interview, but get them to do something in the interview.