You have asked 2 very different questions.
#1 - bid to buy ratio in Cary - looking at the past 6 months of Cary home sales in the 275k - 300k range, the data shows the average is 97% of list price - meaning the final sales price was on average 3% less than what the seller was asking.
#2 What should your offer be? totally different question because now instead of averages you are looking at a specific property - keep in mind that a seller can ask anything they want for a property - it may be priced above, at or below market value
When arriving at an offering strategy there are many variables, how long has the property been on the market, are you competing with other offers, how quickly can you close, what type of loan / down-payment etc
If your question is "What is a fair price for the property?" factors such as what have similar homes recently sold for, how many homes in the same price range are currently for sale versus how many are selling each month - this allows you to determine how many months of supply there is - think supply/demand.
Whenever I work with a buyer client preparing an offer I act as if they already own the property and have asked me to tell them what a fair price would be - I totally disregard what the sellers are asking and start from scratch - going through the same process of determining fair market value for a seller - then I share that information with them compared to what the seller is asking - this is the first step in preparing an offer/negotiation strategy.
Sounds like there's a lot involved to such a simple question right? That's the advantage of having a buyers agent! A good buyers agent can guide you through this process and work at representing your best interests - providing you the necessary information to make an informed/educated decision.
You can find more Cary Market Data on my CaryRealEstate.com website link below.