I tell you something happened to me a pair of years ago.
I received a direct call from an italian guy (i'm italian too) asking me if a domain i owned was available for sale. I replied "yes, of course, but it depends on what amount we're talking about, because this domain is related to a small project i've developing and, you know, changing it in the middle of something would be kind of expensive".
Obviously there were no project or something, i just figured out he didn't do his homeworks, and he confirmed me that when i heard his offer of low €1,xxx , while the domain (a brandable and not great 5L.com) was listed at €499 on Sedo, GoDaddy and Flippa.
In the meantime i was luckily at the computer, and already opened all three marketplaces, logged in and got ready to change the BIN price.
I asked him why he was interested in this domain while i set all the BIN prices at €2,199 . (i know, it might be considered unethical, buuuut if the buyer doesn't do his homeworks.....)
He told me something about his project with his small business, which i replied with interested "a-ha". After that, i told him this:
"Look, your project is way more interesting than mine, more ambicious, and i'm willing to give you my domain with pleasure. I already priced it at €2,199 on most important marketplaces, Sedo, GoDaddy and Flippa, because it is the amount i would give it away. However, i feel like your project would be difficult to develop and starting with the right domain is a huge step, so i can meet you halfway, and sell it to you for €1,800, what do you think?"
We negotiated some more and closed the deal for mid €1,xxx .
I know, a phone call is quite more effective for the negotiation, but while we were talking after closed the deal, he told me something: my domain wasn't his first choice, and tried to negotiate for another domain earlier that week, through email first and phone call later.
He had the feeling the other guy was going to "scam" him, because he replied to the email like instantly, with a way higher counteroffer, and after the buyer told him it was too over his budget, the other guy decided to lower his counteroffer until he basically reached the buyer offer over the phone call, but this behaviour made the buyer suspicious since he wasn't into the domaining world (he wasn't even aware there was a domaining world).
You can answer within a couple of hours but first at all decide your strategy and be coherent with it.
You can also accept the initial offers, but just remember to spend more time with some random talks, make the buyer feels like he's convincing you.