Can I lock a transaction from being used until a particular condition is met I plan to open an ecommerce website from which I will accept BTC as payment. However users dont want to pay with BTC without getting the goods since my site is just starting up. What are the options I have?
Your question indicates some experience with bitcoin, so I am going to be very technical. You may want to look up &quot;smart contracts&quot; as keywords. In the bitcoin world we talk about checklocktimeverify and checksequenceverify, together with some multisig (as escrow service). There are many examples, e.g. here (this is basically what I posted in bitcointalk):
IF
    2 &lt;Alice's pubkey&gt; &lt;Bob's pubkey&gt; &lt;Escrow's pubkey&gt; 3 CHECKMULTISIG
ELSE
    &quot;30d&quot; CHECKSEQUENCEVERIFY DROP
    &lt;Alice's pubkey&gt; CHECKSIG
ENDIF

or something like this:
 if
  &lt;merchant pubkey&gt; checksigverify
 else
  &lt;timestamp&gt; checklocktimeverify drop
 endif
 &lt;customer pubkey&gt; checksig

imho, n-of-m multisig is the easiest form of a contract. Escrow service is the next layer (as in examples above). They can make sure, that BTC is only payed, when a specific condition is met.
And then one can create very specific constructs like:

CHECKSEQUENCEVERIFY: lock some Satoshis until a specific number of
block have passed, before one can use them
CHECKLOCKTIMEVERIFY: lock some Satoshis until a specific number of
block appears (aka my son is 18 years old...), but use a 2-3 multisig
to release the funds in case funds are required earlier

It goes even up to the point where you can create tx spends, where the hash of a condition must be equal to a previously defined value.
I see some limitations when trying to use Oracles (aka data from &quot;outsides&quot;), maybe data from exchanges, or from real live (in case of death).
Some more example in Andreas' book &quot;Mastering Bitcoin&quot; (second edition) in the chapter &quot;Timelocks&quot;.
or here:

https://bitcointalk.org/index.php?topic=1300723.0
https://bitcointalk.org/index.php?topic=1558207.0
https://bitcointalk.org/index.php?topic=1952248.0

or here:

https://www.reddit.com/r/Bitcoin/comments/4kit49/is_it_safe_to_use_cltv_for_recurring_payments/
https://www.reddit.com/r/Bitcoin/comments/4p4klg/bitcoin_core_project_the_csv_soft_fork_has/d4i01he/

and here:

https://en.bitcoin.it/wiki/Timelock
https://en.bitcoin.it/wiki/Contracts