The biggest issue trading forex is you don't know you're enemy. You trade into a dark pool and you don't know who takes the other side of your trade, and unknowingly your spread is adjusted when it suits broker (if broker is a pure market maker)... there are some brokers that offer straight through processing (STP) however I believe there has to be an intermediary as the end bank will not trade without a counter party taking all the risk. Thus there is a straight through to some liquidity provider which hedges before sending the trade to the interbank (if that)... most retail trades don't even make it to the interbank as the liquidity provider/broker acts as a pure market maker and thus has incentive to game your account via spread manipulation or even changing price feed to capture stoploss etc. Thus the positino gets closed on the retail account and broker/liquidity provider pockets the trade with 100% profit. IMO forex trading needs to be shut down for retailers as it is the dirtiest of dirty games... a decentralized economy which would not let a market maker game the system would be pretty cool... spreads cannot be manipulated, price feeds cannot be manipulated, thus EVERYONE is on a level playing-field with a decentralized market.
Thus one of the better indicators is FXCM/Oanda's retail contrarian position indicators which have you go against the retail crowd as they are usually on the wrong end of the deal. This is the result of market-makers/big players fishing stop losses. I suspect this would be the case in any market but it wouldn't be so skewed against the retail trader as it is in forex.
One of the major incentive for market makers in forex is the ability to screw with people's accounts and not have to pay... so some of them are set up in Cypress and other places where regulation is quite thin or non-existent. Although FinCen is cracking down on US brokers I still believe they aren't playing by the rules.. ie: FXCM lawsuits for account/trade manipulation.
Anyone who has traded forex has realized the inevitable... that unless you can trade via the interbank (minimum $1000k USD accounts) it is really fruitless unless you're edge is so great that you profit even in the face of such adverse conditions. I've seen cases where brokers simply "find" reasons to not allow withdrawl... because int he end if a simple claus was not met ie: an automated trading strategy that traded 1 second too frequent would be OK as long as you lose money, but if you made profit and tried to withdraw your funds would be seized and account closed, surrendering all profits, if any.
With a decentralized market all rules are known upfront and no manipulatino is possible...
1) No rule manipulation possible
2) No spread manipulation possible
3) No price feed manipulation possible
All of these things favor the retailers, and not the market maker... although once the traders start to come to a better system market makers will simply show up because of the opportunity to make money via fees... it should be a snowball effect... which is why we are trying to build one big rocket ship to reach the stratosphere, either it blows through or it crashes... it really is as simple as that.