buy price lower than sell price

[bitbillion]

im new to that whole crypto trading but I have recognized a few times that the buy price is lower than the sell price, this usually doesnt last very long but I see it regulary on cryptsy.

Can someone explain that a bit better to me please

thanks

[bitbillion]

noone knows???

i thought there are some professionals here

[DeathAndTaxes]

It should never happen in any credible exchange.  It shows a flawed matching engine.

[OpenPay]

Or a delayed reporting engine.

It's possible that the buy/sell are a little out of sync if the orderbook is deep enough and there is enough activity.  Whereas the matching engine would "one would hope", freeze the DB long enough to match and then release.

One very solid and scalable design for an exchange involves all limit orders going to the orderbook, then the matching engine locking the books temporarily, taking all market orders and matching them first, and only then matching limit orders across the books.  This might result in what you're seeing.

Since you're only seeing limit orders in the order books and last can be either market or limit.
It would resolve itself the next time the matching engine takes a pass across the orderbooks.

Seeing that is a good sign that there is pent up pressure in the market in one direction or the other and would likely mean it's a good time to take a contra position.  Just an FYI for any bot makers out there.

[OpenPay]

the best way i found to do it is buyin on BTC-e and selling at **removed malware link**, i do some cash doing it.

How is that even relevant?

The OP is talking about seeing a buy price lower than the sell price in a particular exchange for a few brief moments of time.
You're talking about arbitrage between btc-e.com and a flybynite site that when I went to it threw up a malware alert in my browser.

[hammo]

im new to that whole crypto trading but I have recognized a few times that the buy price is lower than the sell price

I assume you mean the buy price is higher than the sell price, because generally the buy price is lower than the sell price. Anyway I have seen that on a few trades, but assume it's just a lag. I'm never too concerned and you can't double buy those coins anyway, eventually it catches up. For the volumes that some of these exchanges push through I'm reasonably happy with the service. Mt Gox excluded.