Market Maker or some exchange we don't know of yet that is playing margin on Stamp (like coinarch on Finex).
Stamp does not offer margin as far as I know. Also, it seems to be giving away money with every trade. Odd behaviour for a market maker ...
Can you say more about coinarch on Finex? I don't know anything about that
EDIT: Coinarch is using Bitfinex for it's trades, it allows only a max of 1000usd per trade, with leverage x2 x3...x10
So at times where the price is a bit stable like now, you see many 1000x10/price_BTC orders (or 1000x5/price_BTC etc)
Hmmm, so some leveraged platform that offers max trade size of <50BTC (after leverage) may be taking the other side of the trades and routing them through Bitstamp to hedge. Possible I guess. Still seems odd that every time I have wathced it, it constantly alternates direction -sell-buy-sell-buy-sell-buy- . I am yet to see 2 trades consecutive trades in the same direction with the 49.99bot
(though I admit, I have not watched it for hours on end, nor analysed all the trade data)