Both start by underestimating the scale of the job, mostly because they are only thinking of the large-scale repetitive aspects of it. No need to focus on the detail is there, until it becomes a proper problem?
So, the Guatemalan builder throws himself enthusiastically at the familiar core tasks such as raising the walls, but when it comes to the multifarious little snaglets and clean-ups that will need to be attended to before the project can be declared complete, he at once commences to dodge them or even starts blaming us for changing the original scope. How is the patio drain now blocked by cement his problem? etc.
Once it becomes clear just how much extra aggro the final stage of the project is likely to generate, web-coder and albañil will both start looking to enforce an artificial deadline which will give them a chance of running away and starting the whole painful process over again somewhere else with another customer.
Both are also particularly bad at taking advice from clients. For instance, V told Don R that he should leave the PVC drainpipe inside the hole he'd made for it in the roof of our new store-room. This counsel was duly ignored - years of experience mean that underpaid do-ers always know better than people with a firm grasp of logic - and of course the hole was a different diameter once the cement had dried. Tok Tok Tok soon echoed around the patio as he re-widened it with his tools the next morning. As you can see from this pic, the pipe now fits, but it has some residual straightness issues....