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 49.99BTC (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 watched 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)