When we sold our second house, the people who ultimately bought it for $1,500 less than the asking price initially made such a bad offer (low price, $500 ernest $, two months to get an inspection, contingent on sale of their home, etc.) that we almost refused it outright instead of making a counter offer. In most markets, three months is not an excessive amount of time. Do you know their situation -- building, relocating, etc. Is the house empty or are they living there now? Find out what they originally paid and how long they were there. If I were the seller and $225,000 is actually a reasonable price (Try to determine whether it is.), I would not be impressed with a $200,000 offer but other things such as already having financing could make a big difference. I'm assuming this will not be a contingency, so that should help you a lot.
As someone else said, it is important to remember that unless you have signed a "buyer's agent" contract, the realtor is working for the seller regardless of whether she has the listing. The realtors we have worked with have been so personable that we sometimes forgot that.