@Jay0, warning: long post up ahead!
Hi there! Yes indeed it isn't possible to type up why you think the listing is fraudulent.
Fair enough. More information explaining what led you to flagging may be marginally helpful.
Nevertheless, at least you do get to flag it quickly, easily and then in a stream-lined way, say why you've done so by selecting 1 of the 4 easy options.
I don't have an inside view of the systems but it seems like for the sake of reducing those time and labour dollars that you mention, (a reasonable goal for any business including ABB), they would follow the "build-up" approach.
I.e. if a listing gets one fraudulent flag amid a throng of completed/successful bookings, perhaps there is no cause for alarm. Could have been a series of misclicks, an angry neighbour, a competitor etc. At the very least, the host has the benefit of the doubt.
If the same listing builds up multiple flags from multiple users, coupled with cancelled bookings, low ratings etc then there is most likely a real problem that needs to be more closely investigated.
I know of at least one occurrence where a hosts listings are no longer available on ABB precisely because of what seems fraudulent. There is no big announcement or embarrassment to the individual concerned but see the link below. Apart from terrible reviews, notice how there are no available listings under the host and you can’t even get to them through the links beside each review: https://www.airbnb.com/users/show/84050973
Presumably the listings have been removed by ABB which shows me that they do eventually get to fraudulent listings and hosts.
As I see it, nothing would be more inefficient than spending time and effort investigating one flag, only to find it's a boy who cried "wolf."
Ultimately, if you do strongly sense that a listing is fraudulent and poses a real danger to safety, trust etc., why not call or email ABB? There are multiple threads out there on the best way to do and I particularly like this one from @Dave0&Deb:
https://community.airbnb.com/t5/Community-Help/Contact-Airbnb-A-Community-Help-Guide/m-p/16165/highl...
(Also ABB do have email and ticket support, may not be perfect or exactly what you may wish for, but it does exist. Not defending them, just stating a fact).
Ok, that’s that for that! What a long post! Thank you for reading and happy weekend to you!