The way you ask the question alarms me. Look at the dealership, how many cars are on the lot? How many are within a short drive? How many cars are for sale withing a 50 mile radius? Living in all but a rural area, the answer will probably be in the hundreds of thousands of cars for sale within a short distance.
Despite car dealership acting as this is not true, there is a far less qualified buyers than there are cars for sale. While the salesman will pretend it is not true, you are the final decision maker in a car transaction.
When it comes to credibility, most car salesman have close to zero. I have meet a few that are the exception to that rule, but most have none.
What I would do, in your shoes, is simply this. Hi, you have a X year Honda Y for sale. I will pay no more than $Z for that car. Lets see if we can make this deal happen. Decide your price ahead of time, and don't budge from it. Pay attention to what is important. If they want to charge you $1000 for pin stripping and $300 dealer who cares! All that is fine provided the final price is less than the price you are willing to pay.
If your price is very low, the negotiations make take place over a week or so. You will certainly have to leave the dealership without purchasing the car on the day you test drive it.
Remember that fear and anger are a car car salesman's friend. Don't let them get you emotional. Always remember there are at least a 100 different suitable cars just a short distance away.
In the end, how you got your number is irrelevant and I would point that out. It is just a tactic to get you to question your judgement.