How does the choice of the broker affect results of advisors?

Forex strongly differs from other financial markets. And among all distinctions the biggest, perhaps, is a decentralization. Often people underestimate huge importance of centrality of the exchange and how it helps with regulation, successful development and trade in various systems. As a result the market Forex is decentralized, it is very poorly regulated, and each broker has the stream of quotations, other than all others.
Quite often, when people speak about a depending on a broker, they consider it some rare factor which practically does not affect the general result. Nevertheless, this factor is by no means not so rare, apparently, and its influence can be very considerable – up to opposite results on two different accounts.
So bad in the differing streams of quotations? I suggest to make a small experiment. Write down high and low of value of 5 candles of the period M5, H1 and D1 at three different brokers at your choice. Write down indications of RSI20 and SMA50 for each of these candles. Tabulate these data, for example, in Excel, and then compare. Think as far as indications of the prices on the different periods at different brokers differ and on what periods these distinctions are less considerable; as indications of indicators differ; whether increases or the depending on a broker when using indicators decreases; as the period of the chosen indicator influences trade at different brokers.
If differences between indications of this or that size at different brokers differ more, than for 10% how settings of the advisor optimized on data from one of brokers at trade at other broker will behave? I hope, you will do this simple exercise and will draw preliminary conclusions. And now, after you gained general idea about this, to more than real problem, we will deal with its influence on trade in more detail and also we will think how to minimize a depending on a broker of trade strategies.
Difference in the form of candles
Because of it there is at once a number of problems, some of which are small, and others have a strong impact on trade. One of insignificant problems consists that at different brokers we have different price levels on high/low of candles. It conducts to the fact that some warrants at some brokers are closed on the SL or TP levels, and at others is not present. Sometimes there is enough distinction in one pips, and at us already at one broker the transaction is closed at a loss, and at another in profit. Or, for example, at one broker the postponed warrant was activated, and at another is not present. Nevertheless, it happens quite seldom and therefore it not strongly affects the general result.
On the other hand, the similar difference in streams of quotations (data feeds) leads to the fact that many candles, especially on the younger periods, look at different brokers differently and levels of opening, closing, the minimum and maximum values of candles differ. It results in some differences in the indication of indicators which use such price levels in calculations. For example, you have a strategy, one of conditions of an entrance to purchases on which is finding of the RSI indicator lower than level 30. As a result of inaccuracies of quoting of the price of Close of candles on which there is a calculation of the RSI indicator differ a little, literally on couple of pips. As a result at one broker you receive on the current candle RSI value = 29.99999, and at other broker 30.00001. As the result — at one broker an entrance will be carried out, and at the second – no. Also strategy for crossing of lines, for example, of moving averages, will work for different brokers differently – somewhere crossing of lines will happen earlier, somewhere later. But it, of course, concerns only advisors – at a manual entrance there are no such problems.

Therefore, it would be quite logical to conclude that than the period for work your is less than CU, than it is less SL and TP levels, especially the depending on broker will be your system.
Better to understand influence of this effect and importance of a right choice of a timeframe, think here over what. The difference in 2 points on the hour schedule can mean a difference between candles in 5-10% while on the five-minute period it can reach 30-50%. An example this quite conditional, everything depends on the general volatility of currency pair, but nevertheless it is necessary to be very careful and always to remember it. Especially establishing the new scalper for M1 into the real account.