Hi Pactolus, I know how you feel, makes it hard for retail...

Hi Pactolus,
I know how you feel, makes it hard for retail investors or traders but impossible if you are up against a Tibra trading options while sitting across an internet hub.
My solution to algos is to include a random delay in every trade - say between 5 and 10 seconds which would make that kind of trading a bit of a lottery - won't happen though will it ??

Hi Mintox80,
Mate, short selling is part and parcel of trading the sharemarket (call it speculation if you like, as opposed to value investing) The people who run the markets (and who profit from fees and brokerage) say trading, long and short, gives the markets liquidity and establishes value. They have no desire to cut it out and won't.
It is in fact very hard to detect especially when you realize that shorters have to borrow the shares to sell - its illegal (on most markets) to short naked.

Not all shares are available to borrow, FMG, RIO, BHP no trouble at all but the more illiquid and volatile the instrument is the greater the risk to the lender and his counterparty - in case the shorter defaults, or simply cannot cover.

It is a facinating subject and I have done thousands of shorts on CFDs and probably never made much certainly not as much as on my longs. Then there are the likes of Deutsche Bank who borrow shares, sells them, use the money to buy counter strategy longs so they have two trades based on something which someone else owns and at no or little cost to them, particularly so if they have borrowed from one of their own clients.
And you know what happens to the likes of Deutsche when it goes balls up. Too big to fail? Or is it So big that they must fail?

Finally some history, check this out for your self Mintox, I speak from memory.
The first short was done by a spice merchant in Hamburg centuries ago. His ship was on the way, the demand for pepper was massive so he sold while he was short. The Burgers took him to court intent on loosening his head, but no, it was considered a reasonable and valid trading act given his capacity and intent to cover his shorts.

It is so common now - if you buy an apartment off the plan, the developer is selling short and as is always the case there is a counterparty who assumes some risk.