There are no fees for debit card transactions. FACT!
I have found VISA debit to suffer more transaction failures than VISA credit when it comes to online casinos. This is probably because online casinos do not normally use the additional "verified by VISA" security step, yet the transactions can be pretty large. This is probably why VISA debit gets "trigger happy" over deposits over £100.
Even my Barclaycard locked up earlier in the week, and I thought it was the casino's processor, but next morning I got an automated call from the fraud dept, and I had to verify the last 5 transactions before my card would be unlocked.
What surpised me even more was that around 4 of the transactions had been MISCODED as "computer software store". This was an accredited MGS casino, that of course does NOT take deposits from the US, nor any other country that Microgaming deems as "too risky" because of legislation, such as Spain.
I suspect that it was the VERY large amount spent on "computer software", rather than the string of gambling deposits, that triggered the fraud lock. This was a sudden variation from my usual pattern of spending, which has been 99% online gambling.
This kind of miscoding could get online casinos into a heap of trouble with the EU, as it is considered "fraudulent", and entirely unnecessary for a country where the activity, and it's transactions, are perfectly legal.
This would also circumvent the fees and treatment of the deposit as a "cash advance", and this could anger the banks as they are being diddled out of the revenue, which could cause them to take action against the processor, maybe even the casino itself.
I don't think the UK gambling commission would be impressed either, and such activity could be a problem when it comes to current operators gaining the soon to be required secondary licenses.