If you wanted to sell, say 1 M shares, at .0009 and the b/a was .0008 x .0009, there could be a possibility that your sell order would get filled at the ask, but there is no guarantee. If you wanted a guaranteed sell you would have to place your order at the bid price, and providing they had enough to sell you at the price it would fill. If you placed an AON (all or none) then it would be considered a special order and it would only fill if they had those shares to sell you. If you placed it as a regular limit order at the bid and they didn't have enough shares there is a chance they would sell you a partial amount and then downtick the bid to .0007.
So basically the answer is as long as there is enough shares to sell you, you can fill your sell order if you place it at the bid price for at the least a partial fill and hopefully a complete fill.
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