
I can hear you saying "Use single currency for all accounts" but some books have only 1 currency option and they're too good to miss.
Let's say we have TRY (Turkish Lira) as currency in A book.
All other accounts are euro.
2 days ago, exchange rate was 2,36. (1 Euro = 2,36 Turkish Lira)
Today, we see exchange rate is 2,39. I like to show you how dramatically it will effect your profits..
Let's say you placed 10 bets like this:
Strasbourg 1,50 Stake 5000 TL (2118,64€ based on 2,36 Exchange rate)
Lyon 3,30 (963€)
This surebet gives us a profit of 96,31€ but based on 2,36 Exchange rate.
Okay, let's say Strasbourg wins and exchange rate increased to 2,39.
According to 2,39 exchange rate, your risk on Strasbourg becomes 2092€!
And your proits drops to 83€!
Imagine this scenario with 100 bets. It means -1331€ net profit.
Can you imagine the loss in more dramatical swings such as 2,30-2,40?
Of course, the contrary scenario is possible. If currency rate drops, then it's good for you as long as the team you bet with your local currency wins.
Or euro may go up and if teams which you bet at Pinnacle/Betfair/Sbo are winning (which is very unlikely, lol. You're doomed to lose in these) then your profits will increase.

Here's the solution I found for this. I keep most of my cash in Euro. Therefore, when Euro gains value; Yes, my profits will be decreased a little bit but my overall balance will get more value since Euro goes up!
Let's say you have 200,000€.
If Euro is 2,36. Then it makes 472,000 TRY.
When Euro jumps to 2,39, it makes 478,000 TRY.
+6000 TRY profit. Not bad.
Of course, using single currency for all books means no headhache but as I mentioned, some books are too good (and gold) to miss. Therefore, sometimes you have no option.
Some arbers use a fixed exchange rate but I don't think it's a good idea. Me, I'm using daily, actual exchange rate. Euro is 2,39 today, it drops to 2,38 tomorrow. Then it climbs back to 2,39 next day. This way, you can get a more average number I guess.
I wish everyone a profitable week, Good luck!