Sorry, so I'd meant to reply to this thread with more "evidence" of what this looks like, and sure enough it still happens literally every day at some point in the last 30 minutes of trading. Here's are the Bids/Asks at 3:43pm and then 7 minutes later at 3:50pm. These 1-lots show up like clockwork every. single. day. On exactly the same contracts. So is this what fraud / market manipulation looks like? (**BTW, the spreads aren't usually this large. There'd been some corporate actions and earnings stuff that had the MMs setting crazy-wide spreads; they're usually in the 30 to 60 cent range, and STILL the 1-lots show up)
It could be the market makers de-risking while still making a market. Again you didn't say what the security is, but in many markets the market makers are required to maintain a bid/ask at all times as one of the terms that allows them be a market maker. The loophole is that the spread and the size aren't specified. This MM may be responding to uncertainty at the end of the day by reducing all their asks to 1 lot, that way even if they get hit it won't impact them much? The fact that all the other bids/asks are 10 also points to a book that's entirely made up of MM orders.
Feel free to check it out on your own - security is AYA (on TSX, not US-side). Happened again today, just like it always does. Don't think it's the MM reducing their asks to 1, b/c when i look at the market depth, I see the exact same 10-lots as existed at 3:43pm still there and haven't budged...it's just a bunch of NEW 1-lots that appear in between the existing bid/ask.
Should have indicated it was the Toronto Stock Exchange in the OP, the US and Canadian are two totally different option markets. The volume and open interest must be very low on those options.
That does appear to shoot down that theory. Thanks for naming it though, I'll take a look tomorrow afternoon. Interesting stuff even if it does end up with a benign explanation.
So...is this basically what stock manipulation looks like or what? Same 1-lots show up on a daily basis and have been for months. Always in last ~20 mins of trading.