It's your own responsibility to keep records backed up. Do you just keep your bitcoins in once place and if they get stolen, lost or destroyed you're shit outta luck? You'll have to check with your local tax authority on what excuses they will accept, though. I'm sure if your house burns down then they would make an exception for that, but not if you just claim "my dog ate my tax records" or "I lost them".
Well this is something you'd have to tell them and hope they understand. It certainly isn't an excuse for not paying taxes though, otherwise everyone would do it. If you can prove an exchange went down or lost your details then I'm sure they'd understand, but you should be keeping records as soon as you make the transactions to avoid any issues further down the line.
When I put my coins in Mintpal to trade I was waiting for confirmations to end, I went to sleep, woke up next morning, and then the exchange had disappeared, I was waiting for confirmations to take the trading history screenshot. This is plain bad luck, not a fucking excuse, it's what happened. It's more like what excuses they will find to confiscate my money.
Also some exchangers are straight scams, like Livecoin which says (in TINY font) "we only save records for the past 30 days". A lot of people didn't see the tiny font, now they lost many trading records, until they realize the stupid idea of not keeping records permanently or at least having it in big font. C'mon!! fuck that. These things just force people to hold these coins and never ever report. What would be the point anyway? you are already screwed.
How do any other businesses pay their taxes? How does somebody who sells cakes out of a cake shop prove they sold as many cupcakes as they claimed? How much did they actually spend on sugar and flour? You keep records and receipts. Businesses keep spreadsheets of in goings and outgoings and pay taxes on their profits. People can just make up a spreadsheet and receipts of course, but if you ever get audited you'll have to provide reasonable proof to back up your claims. Keep records of every bitcoin you receive and every time you sell them. Take screenshots of your transactions and you usually get some sort of email receipt when you cash out coins and that is good enough proof. You people seem to be looking for excuses to try get out of paying taxes, but believe me, your tax authority will not accept any of these as valid excuses. You'll get fines and possibly even jail time if they can prove you have purposely avoided paying taxes due and all the excuses of "I didn't know what taxes to pay", or "it's too difficult to know how much I should be paying" will just be laughed at in court.
I have all of my transactions in Bitcoin Core, I took screenshots of most transactions and trading history, but I was unlucky with Mintpal. Also I have some coins mixed, these I understand I can't never sell now.
Im not looking for excuses to not pay taxes, I just don't want them to find excuses to fuck my hard earned bitcoins up by stealing them from me because some unlucky moment which made me lose some of my trading history. Since there are no guarantees of what happens in this situation, it's safer to hold and look for other people's experience in the same situation, don't be a guinea pig for the goverment's legislation on crypto guys.
Again im not trying to not pay taxes, understand the situation here.
And if governments don't cooperate, they will just scare away holders which will leave to more friendly jurisdictions in this matter, and they will miss on all these juicy taxes while the friendlier country benefits.