Ok, they represent the same value. But sometimes they look the same. Reversed and encoded in base 16 just happens to get the same result as double SHA256?

Are you sure you are looking at correct values?

Here is an example transaction

link on block explorerThe raw bytes of this transaction is:

01000000010000000000000000000000000000000000000000000000000000000000000000ffffffff0704ffff001d0104ffffffff0100f2052a0100000043410496b538e853519c726a2c91e61ec11600ae1390813a627c66fb8be7947be63c52da7589379515d4e0a604f8141781e62294721166bf621e73a82cbf2342c858eeac00000000

You can use this online tool to compute SHA256 of hexadecimal input:

https://cryptii.com/pipes/hash-function click on the drop down dots and select duplicate to compute it twice. It should look like this:

https://i.imgur.com/LWXpRIA.jpgAs you can see the result is going to be:

982051fd1e4ba744bbbe680e1fee14677ba1a3c3540bf7b1cdb606e857233e0e

Now if you look at that link from block explorer you can see that the txid is:

0e3e2357e806b6cdb1f70b54c3a3a17b6714ee1f0e68bebb44a74b1efd512098

that is the hash result in reverse.

edit: Of course I forgot about SegWit, if the transaction has any witness, it has to be stripped off before hashing it as @achow101 pointed out.