Average No b. Not enough manpower. Post-synthesis QC methods are too expensive. There is no need. Automated DNA synthesis is generally reliable.
Failure rate is very low.
Oligonucleotides of low quality are still usable in forgiving oligo-dependent experiments. Failure can be determined by QC of some of the oligonucleotides. One that is not as good as most oligos that you deliver. One that does not work in the user's experiment. One that has a low yield of the product.