It could be done even easier. There are HTML and CSS verifiers on the net, why not a search engine verifier? I don't think Google will make such a service available--because with a Google certified verifier it would be too easy for SEOers to reverse engineer Google's algorithm--but an independent service tuned with knowledge from people on this board could be made very accurate IMHO.
There are many smart programmers around here. Could be a nice project to set up such a system. Parameters which can be taken into account could be "percentage of reciprocal links", "percentage overlap with ODP", "number of content pages vs. number of directory pages" etc. By feeding this system with enough both healty and banned websites, I believe it is possible to tune such a system to give fairly accurate answers.