<p>Replacing transactions without confirmation is relatively easy.
I would tag every transaction without confirmation as "suspicious".</p>

<p>RBF is a policy and miners could also replace transaction that do <strong>not</strong> sign opt-in-RBF.</p>

<p>Best way to check if a 0-conf transactions will be mined soon:</p>

<ul>
<li>check nSequence number (only accept 0-conf if nSequence number is INT_MAX)</li>
<li>check the transactions fee-rate and compare it with your estimated fee (requires a mempool/bitcoin-core)</li>
<li>Calculate the risks: every 0-conf transaction can be replaced/double-spent! High value items should not be "dispatched" &lt; 6 confirmations (IMO).</li>
</ul>

CC BY-SA 3.0
2016-06-01T14:56:22.710Z
Thanks. Just to be sure, did you actually mean: if nSequence number is INT_MAX or INT_MAX-1 ? (that's 0xFFFFFFFF or 0xFFFFFFFE). If I'm not mistaken, the opt-in RBF is flag consists of an nSequence **below** INT_MAX-1 ?
RocketNuts
CC BY-SA 3.0
2016-05-30T16:21:11.947Z
2016-05-30T16:21:11.947Z
Jonas Schnelli
<p>When looking at Bitcoin unconfirmed transactions, I'm trying to distinguish between txs that are likely to confirm (whether that be in the first next block or in 2 hours) versus txs that are likely to be replaced, or never to confirm at all.</p>

<p>Obviously, txs with the opt-in RBF flag fall in the latter category. </p>

<p>But I guess there are other criteria, such as:</p>

<ul>
<li>having an extremely low fee, or even zero fee. </li>
<li>Having lots of dust outputs. </li>
<li>Depending on unconfirmed inputs.</li>
</ul>

<p><strong>Anything else I should take into consideration?</strong> What other factors could make a tx less likely to end up confirmed? </p>

<p>For example, besides dust output, do dust (i.e. many small) <em>inputs</em> make a tx less sure to confirm? (other than more inputs causing larger tx data, thus resulting in a lower fee when measured in satoshis per KB)</p>

CC BY-SA 3.0
2016-05-22T23:29:34.907Z
Classifying 0-conf transactions based on whether or not it has RBF or any of the above-mentioned characteristics is inappropriate. A transactions that is least likely to be double-spend or confirmed is one that incentivises miners least to include into a block. One could equally argue a transaction that satisfies the negation of all your above-mentioned properties would still be "suspicious" if miners were purely incentivised to mint based on transaction fees alone.
rny
<doublespend><unconfirmed-transactions>
What makes an unconfirmed tx 'suspicious'? (likely to be replaced or never confirm)
RocketNuts
# What makes an unconfirmed tx 'suspicious'? (likely to be replaced or never confirm)

(Asked by: username_0 on 2016-05-15)

When looking at Bitcoin unconfirmed transactions, I'm trying to distinguish between txs that are likely to confirm (whether that be in the first next block or in 2 hours) versus txs that are likely to be replaced, or never to confirm at all.

Obviously, txs with the opt-in RBF flag fall in the latter category.

But I guess there are other criteria, such as:

* having an extremely low fee, or even zero fee.
* Having lots of dust outputs.
* Depending on unconfirmed inputs.

**Anything else I should take into consideration?** What other factors could make a tx less likely to end up confirmed?

For example, besides dust output, do dust (i.e. many small) *inputs* make a tx less sure to confirm? (other than more inputs causing larger tx data, thus resulting in a lower fee when measured in satoshis per KB)

**Tags:** doublespend, unconfirmed-transactions

> **Comments:**
> **username_1**: Classifying 0-conf transactions based on whether or not it has RBF or any of the above-mentioned characteristics is inappropriate. A transactions that is least likely to be double-spend or confirmed is one that incentivises miners least to include into a block. One could equally argue a transaction that satisfies the negation of all your above-mentioned properties would still be "suspicious" if miners were purely incentivised to mint based on transaction fees alone.  

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## 1 answers

### Answer by username_2 on 2016-05-30. Score: 2

Replacing transactions without confirmation is relatively easy.
I would tag every transaction without confirmation as "suspicious".

RBF is a policy and miners could also replace transaction that do **not** sign opt-in-RBF.

Best way to check if a 0-conf transactions will be mined soon:

* check nSequence number (only accept 0-conf if nSequence number is INT\_MAX)
* check the transactions fee-rate and compare it with your estimated fee (requires a mempool/bitcoin-core)
* Calculate the risks: every 0-conf transaction can be replaced/double-spent! High value items should not be "dispatched" < 6 confirmations (IMO).

> **Comments:**
> **username_0**: Thanks. Just to be sure, did you actually mean: if nSequence number is INT_MAX or INT_MAX-1 ? (that's 0xFFFFFFFF or 0xFFFFFFFE). If I'm not mistaken, the opt-in RBF is flag consists of an nSequence **below** INT_MAX-1 ?  

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