Athletes competing on an elite level should certainly have their sex verified. In almost all cases this will be less intrusive than the anti-doping tests they're required to do; a simple cheek swab is sufficient for screening via karyotype analysis. And the blood samples already taken for drug testing can be used to measure testosterone levels for this purpose.

Only if there is an anomaly might further investigation be done, with the athlete's permission. No dissection is needed - at most some imaging to determine internal anatomy may be done by medical experts.

This is already the policy adopted by some sporting bodies, and was essentially the process used with the athletes I mentioned in my earlier comments to observe that the sex of each is male.

Ideally this would be done as early on in an athlete's career as is practical. It only needs to be done once, as a person's sex cannot change, and for most will be a straightforward confirmation of what is already known. Otherwise, it's better for the athlete too, to know sooner rather than later if there has been any anomalous development.

I would suggest you examine the public information on the aforementioned male athletes more closely. In particular, 5-ARD is an indisputably male condition; the mutations in the SRD5A2 gene that cause this have no effect on female sexual development. This is fact, not opinion.