So she's 18, fairly uneducated when it comes to sex, and could potentially earn 1,000,000 euros by having sex.

What is the issue here? Is it that something like virginity should be sacred? Sex should be sacred? Is it the potentiality of her contracting a disease or some psychological harm (for lack of a better term) over this decision?

I mean, today, a lot of things fall into the ethical grey area whereas even 10 years ago they would have been either wrong or right. Prostitution as one of those things proven by the mixed state of its legality in different locations across nations/societies.

I don't think that, (who?) Phillip and Holly's concerns here are baseless, either, but at the same time, certain precautions could be taken to mitigate them: test the highest bidder guy for diseases, (some people are saying sex slavery is a danger here) and as far as him turning out to be a criminal with violent intent, I don't think 1,000,000 euros changes hands so easily; no matter how anonymous the bidder may want to remain in all this, criminals usually commit crimes when they think they can get away with it, her disappearance would raise a lot of eyebrows in his direction... i.e. forget that whole argument.

So is the issue with this whole thing something else entirely? Assuming the aforementioned precautions (and more) were taken and she was as safe as could be, would there still be an issue?

Like is it that she'll regret it later? Or what? I don't want to make it into a sex-war or anything like that, but if a man wanted to sell his virginity and could get paid 1,000,000 euros, would it be as big a deal?

I it her circumstances? That she's doing it as a last resort? I mean, what if she just said, "I just want a lot of money." and gave no further explanation. Would that be less concerning than this situation? Probably, right? So is that the issue?