I've done it a few times since I started collecting in the early 2000s and it never hurts to ask. Some will entertain offers and some won't budge, no matter how many years it's been sitting. The biggest discount I got by asking is about 15%. Take the chance if you're serious about a coin.
Some customers will contact me - for the most sellers this is no problem, if you send a real price request. For a long time a customer offer me around 300 USD for a 900 USD coin. Thats not a offer, thats without any respect for me. I never answer and blocked him for any futured possible deals A tip from me. Sometimes customer reports, that they will make a offer with the direct contact button at VCoins and they never get a feedback from the seller. Sometimes - I didn’t know why - this contact not work and I don’t get often the request from the customers. It was better, when you go to the TERMS of the seller and search there for his email adress. Write him directly a email! That’s better.
Making an offer through the platform has costs, but also some level of protection (whatever the platform offers). Making an offer directly avoids the fees, but also doesn't offer the same protection. Do your diligence and work with dealers you or others know and trust.
I started a thread a while back related to this topic. I was concerned with the fact that different cultures have different ways to do business and was it offensive or rude to ask someone for a discount in certain cultures. I feel like American dealers pretty much expect customers to ask but I don’t know about others.
If you know/trust the dealer, you can also offer to pay through something like TransferWise which cuts out forex fees and makes the transaction easier on a non-US dealer!