The blame is usually misallocated
When a wall lands in the wrong place, the client's first conclusion is that the drawing was wrong, and the architect's first conclusion is that the contractor cannot read. After thirty years of standing between the two, the honest finding is that both are usually wrong, and the useful question is a different one: how does this contractor process information, and was the building's information system designed around it?
The four contractor patterns
The district's contractors sort into patterns you can identify inside two site visits.
The memory builder works from what you said, not what you showed. He will nod at the drawing and build from the meeting. His work is good exactly as long as the building is simple, and drifts as soon as two systems meet. With him, the drawing must be delivered as spoken instruction: walk the sheet aloud, weekly, at the wall.
The mason's contractor is a mason who started taking contracts. Excellent at finishes and levels, weak at sequence. His buildings look right and open late. With him, the schedule is the document to enforce; the drawing he can be trusted with.
The rate man prices everything and reads nothing. He will execute the drawing literally, including its errors, and claim every ambiguity in his favour at the bill. With him, the drawings must be ambiguity-free, and they will not be, so supervision becomes contractual: every visit's corrections written, signed, costed.
The partner reads the sheet, asks about the junction before it is cast, and flags a clash before it is built. Rare, and worth keeping for decades. The recorded experience of this practice is that most site defects happen when the contractor is the client's own man, chosen for relationship rather than fit, because nobody can supervise their own relative honestly.
What the client controls
More than he thinks. The contractor pattern is not fate; it is managed by the information system around the site.
One meeting a week, at the site, standing at the work. One sheet per trade, as in the field note on readable drawings. One written line after each visit recording what was corrected, so the memory builder has a memory and the rate man has a record. Payments released against stages actually verified, not against complaints withdrawn, which is what the stage structure on how we work exists to enforce.
The uncomfortable summary
Your contractor is rarely the villain of your project. He is a pattern, and the pattern was knowable in week one. The drawing is rarely the villain either; it is a document whose readability was decided before construction began. What decides the build is whether somebody stands on the site weekly, knows both parties' jobs, and corrects the gap between them while it is still cheap.
That job has a name. It is most of what a fee buys, as set out in What a fee actually buys, and it is walked in detail in Two visits a week.