When you see them starting at $1 or $50 you can be assured they're fake.
Looks like you're catching on. Nobody sells a site that makes $200 a month for $400. Real sites that make $200 a month start high and have a high reserve ($1000 price range). Most revenue claims on Flippa are fake and sites are sold by newer selling accounts. They report fake revenue (Flippa actually encourages it) and after they accumulate a bunch of bad feedback they just make another account and start all over. In the meanwhile it's the buyers getting scammed.
A website making $200 a month has a minimum value of $1000. When you see them starting at $1 or $50 you can be assured they're fake.
In an auction setting, starting bid has nothing to do with the value of the merchandise (in this case, website). I have often recommended my clients to run "$1 start, no reserve" auctions, and as brokers we have done the same ourselves.
It's up to the bidders to do their due diligence and decide how high they wish to bid, and these bids are what dictate the market value of the site/business.
Obviously no decent site that makes $200/pm would ever sell for $400 (as per OP's example), unless there's something very wrong with it. Most of listings of this kind are simply scam attempts and a winning bid of 2x monthly revenue clearly shows that it hasn't worked. But once again, the starting bid has absolutely nothing to with the actual value of the site.
No disrespect but you have a lot more confidence in Flippa buyers than I do if you're advising clients to list $1 start / no reserve for a $1000+ website. I suppose if you string these out to 10-30 day listings and pay Flippa premiums for better exposure you might catch enough views and action to make a safe bet of success.
I guess a non-featured 3 day listing claiming $200 /pm starting at $1 NR is more safely a scam bet, rather than saying all money making sites starting at $1 NR are most likely a scam.