Let's clear up one thing: high leverage does NOT a bucketshop make. Just because an exchange is offering high leverage, does not mean that they are betting against you.
Bucket shops are problematic because at their core, the owner of the "exchange" is taking the opposite side of your position.
Legitimate exchanges, on the other hand, have an orderbook which matches counterparties who are customers of the exchange. Thus the high leverage is being provided between counterparties who put margin down to back it up.
Can I trust bucket shops?
The principle they rely on is that at high leverage, most traders lose money. Most traders are unable to overcome the psychological limitations of being human which make one behave irrationally in times of market volatility. This allows a rational marketmaking system to be consistently profitable in the face of what otherwise would be chaos.
The bottom line is that the exchange being counterparty rather than providing an orderbook to match counterparties is simply a business model difference. There are some exchanges with orderbooks which are not highly trusted, like OKCoin. They are known to run bots which fake volume, and are suspected to hunt margin calls because they have bots taking the other side of many trades. This in effect creates a bucketshop incentive in an orderbook exchange model. So trust each company on a case by case basis. Look them up on BitcoinTalk and see if there's any complaints. Always do your research.