That's quite an obvious problem, buying with vouchers, and you can't blame casinos for doing SOW in that case.
BUT, the problem that players are finding is that most of the Malta-bassed casinos are using an arbitrary threshold, some as low as £2000.
This threshold isn't based on a period of time, but on the lifetime of the account, it's also not just on deposits, but the turnover of the account, including withdrawals.
Which is why a lot of players are getting caught at the withdrawal stage, since a largish withdrawal can take them over the threshold.
Therefore, some players who ARE depositing and withdrawing to the same method, Visa for example, who aren't spending excessively. But are making small deposits, weekly or even monthly. Are still falling foul of SOW requests when they get a decent withdrawal. Or when the threshold is reached through deposits, which might be as low as £20 a month over a several years.
That's where the resentment comes from. The Malta-based casinos using a blanket policy, rather than actually assessing the risk first