I've heard from an AM that it's when you hit 1k, but in my experience my accounts get shut down way before this, usually some time after I hit the $350/day mark.
Are there any other opinions as to when they go back to take a closer look, and what exactly are these FB reviewers doing?
What are you running exactly on facebook that you get your accounts shut down so fast? Maybe you should try a more safe picture and / or adcopy.
I noticed the same thing, after $350-500/day a reviewer take a closer look, also if the CTR is very high.
.2 CTR or higher then your ad is automatically flagged for review. I know this cause I just got an ad approved and I had a .2 ctr
Immediately after running it for 5 mins it got retro-disapproved. Happened like 5 times now. I have a second ad thats a .1 ctr and its been alive for a couple days now. Those bastards are getting more and more strict everyday.
Almost all my bans happend after i spend more than 1000 USD/day.
I use risky images. High CTR. But almost no retro-disaprovals.
I advertise international (non US).
I never advertise in US either. Its all UK, CA for now... still get retro-disapproved :/
Not sure what the exact level is, but there's definitely reason to believe the more you spend, the more interested Facebook gets in your business.
I would assume that there's some kind of time-controlled quality score attached to each account. I've got a Facebook account I've been using for about 4 years now and if I blow up over $1000/day on that, I'm guessing it's not as suspicious as the guy who registers an account at 9am and is splurging thousands of dollars by the mid-afternoon.
transaction velocity...is all I am gonna say 
My last FB ban was triggered by high CTRs. I had a couple new ads that were doing around 0.25% CTR and FB started checking my campaigns. They checked an old paused campaign that I had redirected to a skin care offer and hadn't run in months. They didn't even bother to check my active campaigns, they had what they needed.
I'd say high CTR ads, reported ad, account history + spending spree.
Main variables of account reviews:
- High CTR,
- High increase in daily spending, and
- Overall spend of ~$500 daily
and your account will be looked at quickly.
Other variables are the niche your running in, high bid increases, lots of active/pauseing of the same ads.
Also i'm almost 100% sure reviewers will tag your campaigns and/or ads when you initially upload them if they pose any risk at all. Then those ads/campaigns will be double reviews even if your campaign/ads are active. I feel sometimes the 2nd review will clear your name and they untag your ads/campaign as risky or sometimes leave it in for futher inspection at a later date.