Credits
We do have a T&C stating that can only be used by UK residents but were first reluctant to enforce this extra rule. We do now block opening accounts in if the country of residency is not UK.
About the exchange rate overcharge it's a real problem but not in our control unfortunately we therefore try to handle as much currencies as we can /$//RRub for our key markets. But at playtech casinos you do not play with credits but in your currency so there is a difference, especially what you mentioned with 1-3 big bets.
While the casino recognises currency, my argument is as follows. if I deposit $200, I suffer exchange losses, but have to wager only 12x, however if I deposit 100, which is roughly equivalent to $200 (give or take), I have to wager 25x - not because 100 is more than $200, but because I am from the UK. This indicates to me that you have an "issue" with players from the UK, whatever that may be, and I play at casinos that do not differentiate between UK and non-UK players with respect to how much wagering is applied to any promotion. I would play though, if they offered bonuses up to $200, but restricted it to the equivalent 100 for UK Pounds.
While you have expressed concern about a couple of big bets being used to attack the bonus, you have pretty much put a stop to this with the prohibited games list. Video Poker seems an oddity, a big bet here is far less likely to result in a big win from a big bet unless you are pat dealt something really good on your first hand, which is about as likely as hitting big on your first slot spin. The only remaining possibility of making big bets is the slot games, $400 (including $200 play bonus), could be used at, say, $25 or even $50 per spin on a slot with a good mid range paytable, and hoping for a decent hit. Given enough accounts, this would work in the long term, yet would still be seen as a "loophole" by advantage players since you prohibit a large list of games to prevent big bet possibilities rather than prohibit the big bets themselves.
Most players that seem "connected" in attacking the bonuses are not in "evil syndicates", but have joined advantage play forums, subscribed to "premium content" areas of bonus whoring websites, or even bought the casino eBook from eBay. The information needed to attack any kind of bonus you could possibly think of is available for free on the Wizard of odds website, although a degree in mathematics is helful for understanding the finer points.
Advantage players do not necessarily need to understand this though, they need to be able to follow instructions to the letter, however bizarre they may seem. This is why you get a number of new accounts who deposit the same amount, play the exact same strategies on the exact same games, and withdraw at the earliest opportunity, probably never to return. They are simply following a list of instructions from their chosen portal. It isn't like card counting in a B & M casino, where it takes time and effort to develop the skill to get it right, mainly because you are not allowed to bring in computers to use while you play at the blackjack tables.
Fraudulent players are a different matter, and should not be confused with mere "advantage players". These frauds work because one player uses as many accounts as is needed to get the big advantage hit. They could win even with the most draconian list of restricted games (they would just need to try more often with more accounts). What you see as syndicates are a more sophisticated play on this, where each account is created with genuine and verifiable details, but these will often be opened from the same place, and this place will often not match the account details. This is why it is unwise to register anywhere other than your home PC, but T & C tend to explain this in a rather technical manner, waffling on about IP addresses, MAC identifiers and so on, most players will simply read, but not understand a word of this, and assume it must not be a problem - so go ahead and register at work/university/friends house - something that could get them mistakenly flagged as a fraudulent account along with those accounts that really are created fraudulently.
It is far better that such terms are enforced by the software as soon as players attempt to register, and I know that Playtech software can do this instantly if it detects such registration breaches, producing a "contact support" message and locking the account temporarily.
The mention of a "Playtech blacklist" is interesting, and illegal under data protection laws where a player given no opportunity to correct the information. While this can happen with credit reference agencies, data protection laws give the person the right to see their entire file, and to demand wrong information is corrected either by the offending company or by them adding their own disclaimer to their file. I doubt the Playtech blacklist adheres to these rules, and for much of the time the industry has tried to insult our intelligence by claiming these "rumours" of industry wide blacklists are without foundation. It seems possible to get on these blacklists not for fraud, but just for winning too much by playing the "wrong games", usually card games.