I love people moaning about builders.
Because its always their own fault generally by trying to get it on the cheap. Not always but more pften than not.
Only five percent of any building problems happen at the chalk face. 95% can be directly attributed to the stupidity and lack practical knowledge of people like achitects and engineers or clients not knowing what they actually want.
If its wrong, or missed of the plans, dont expect to get it for free if its takes more time and materials as a result, then expect to get charged. HEAPS 
Good and cheap just dont go together anymore than a new merc can be bought for the same price as an old skoda.
Trades people aint there to do favors just because you have a shity old house which will cost a fortune to fix, expect to pay for it
If a builder comes to look at the job, he should allow for the time it takes to look at it and price it in the quote. Its called "the consumer pays" its a business afterall.
If your looking for a cheap price then you,ll most always get a dodgy builder or trademan who will take short cuts
The only reason people give cheap prices is because they know they are useless and it will be a rough job, or they dont have enough work, the reasons being that they are useless anyway and word has got around so no repeat business
No one wants to fix up someone else's shit work, especially when the homeowner has "had a go at it, and fucked it up 
expect to pay heaps to put it right
The smaller the job, the higher the cost, so expect to pay for, travelling time, lunch time, sitting around having a fag time, phoneing up your mates, time, and snooping round your house time. 
Always best to get someone from a firm that employs trade people as staff. May cost a bit more but the results are generally much better.
Dont be a tight bastard, get your hand in ya pocket.