I will take your bait and be the first one to answer, offering you my HONEST opinion.
Will you return back?
Legally, if you receive money in your bank account it's incorrect to keep the value. Ethically, it's incorrect to keep it.
Yet a sum of 100 BTC is equivalent to some £300k / $400k using present BTC value.
The 'good/bad' part about Bitcoin is that it's not like a bank, therefore technically you
could keep all bitcoins.
My ethical values would push me to return back the BTCs, however by applying a different
methodology. Do you know what happens if you find a suitcase with $100k on the street and you return it?
In most countries you keep up to 10%. Therefore, I will probably enter in contact with the person (they
are more likely to be looking for me and enter in contact) and explain them about my
offer. They either gets back 90 BTCs or I will leave these bitcoins in the wallet for ever
until it reaches $20k/BTC again. When this thing happens, I will return $400k and keep the rest
good points