> Bitcoin is very careful to only order transactions by what block they are in and not where they are in the block. Transaction order within a bitcoin block de

> Bitcoin is very careful to only order transactions by what block they are in and not where they are in the block. Transaction order within a bitcoin block definitely matters: if transaction b spends the ouput of transaction a within the same block, then a MUST preceed b. Also, the coinbase transaction must be the first. Other than that the order is arbitrary.