Your trading profile and how it might impact on quotes given.
You have to understand that because 80% (I saw the figure somewhere) of all SB trades are made over the internet SB/CFD companies can very easily monitor the activities of each of their clients. Thus, when you enter a trade their trade management systems can easily identify whether you are typically "successful" or not. It would be unreasonable not to expect them to manage their position/risk. In otherwords, every time you trade you leave very clear footprints/trails. The long term viability of these SB/CFD companies is underpinned by analysing the profile of their clients.
Remember, these companies are basically offering the ability for their clients to trade.
They are not taking views on the direction of the market/stocks. (Despite what it looks like)
Obviously if you are "successful" that would suggest that they would want to hedge your trade before accepting your business (because they do not want to lose money by taking a view on direction of any trade).
Unfortunately, most clients are not "successful" and as such there is no need for SB/CFD companies to hedge their trades on balance ( a lot of client trades will effectively cancel each other out) . So for the vast majority of us, as long as we are not attempting a large trade, we should get pretty instant quotes.
Remember the source of the SB/CFD company profits comes from the spread quoted for each trade.
Whether this trading profile knowledge impacts the quote given to each trader, I leave up to you. However, one reason why you might get a re-quote is that the software has identified you as "getting it right" and they are trying to hedge your trade before accepting your business.
Hope this helps
PS: I have no connection to any SB/CFD other than as a customer.
However, I do know one of the CEOs who in a conversation commented on how they managed their business.