225,000 is 91.8% of the list price. Is this too low, you ask. Like Tony said, you need comps, good comps that are as close to the property you are interested in as possible. Other things to take into consideration, is days on market, condition and location, and how desireable the home is to you.
Are you asking for assistance, like closing costs? If so, taking all the above into consideration, you should make the offer as enticing to the seller as possible. If you are asking for closing costs or down payment assistance, then essentially the seller is "financing" part of this for you, or in other words, giving you a percentage of their proceeds so that can buy the home.
Buying a home is a big step in your life. Take all the above into consideration, and then go one step further. Remember that if you come to an agreement on this home, chances are you will want to sell it some day too. So, try to think from the seller's side as well, and if you are comfortable with your offer, make it. Be prepared to walk away or negotiate when you make it, in case the seller doesn't agree with your offer.
Also, if you are not working with an agent, or even if you are - get your inspections. This can save you money in the long run. Termite inspection is mandatory if you are getting the home financed. Also get a whole house inspection from a reputable, licensed inspector and leave your options open for radon and mold. If the home is several years old ask for a home warranty.
I hope this helps and good luck with your purchase! If I can be of assistance, feel free to email or call.
If you are working with an agent, ask the agent to pull the comparables for that area. Finding GOOD comps for the area will help you determine the best offer you can make on this home. If you are not working with a buyer agent, find one that will help you get this done. If you need more help let me know. http://www.TonyBrust.com