OK my ART experience has concluded. From five contractors...

OK my ART experience has concluded. From five contractors interested in a job where I stipulated there is no ceiling on the budget, so as not to scare off any quality providers, two gave firm quotes. The other three wanted to deal outside of of Airtasker. So Airtasker does some hard lifting with associated costs to create a market place only for it to be circumvented. The ad also attracted interest from providers who did not perform only this task/trade which is not what was wanted.
If roughly 28% is added to the costs when compared to mainstream services, this is unappealing to a buyer and a barrier to a supplier to win the work. A buyer either get's a 30% margin once GST is added, or starts off a job with someone who is dishonest. Not very appealing is it?
This experience was for a trade that you can easily compare once you have enough quotes. Other random stuff posted on ART may be very different and likely a better outcome for buyer and provider. I doubt I would try this service again.
As a business investment I don't see any barrier to competition and there are challenges as outlined above.