My thought process, if I were in your shoes:
1) Is the watch keeping good time? Not needed to be within COSC, but it should not be running in a faulty manner (i.e. worse than a Seiko's rated specs). If YES, suggest not to service. If NO, suggest to service.
2) Why #1? Because it is one thing to sell a watch that needs servicing to reach COSC standards, it is another thing to sell a watch that is running in a faulty manner. The first, I think any normal/rational buyer that isn't too picky would not bother. The second, EVERYONE would be mighty pissed if they now have to send in the watch for it to work normally, and there is also no way to check on this prior to the purchase. Alternatively, you could price it lower in recognition of the need for service, but this will turn off many potential buyers because this could mean that their cost could range from a simple servicing to a massive overhaul. They are now taking a lot of risk. The funny thing is that even if it is running OK, the watch could break down the next day and they would face the same risk. But that's just human mentality for you.
3) If you service, you will definitely want to pass on the costs to the buyer. If everything seems OK, and your watch is not that old anyways, why bother? Leave the choice to the buyer. You also reduce your pool of potential buyers by jacking up the price right away.
4) Lowballers will just lowball, nitpicking at servicing (or lack thereof) is just one of their many tools. As a friend once said, all you need is that ONE willing buyer.
Hi bro, thank you for your great reply. Currently, the watch is keeping good time and it’s also under warranty by Rolex till Sept 2021. I guess it won’t be worth the service and not even the polish. If I were to sell I guess I would just leave it up to the buyer if he/she wants to get it polished up. I’ll probably add a very slight discount too to factor in the price of polishing.
Anyway thanks for your reply and I will definitely consider all options carefully.