Short answer - you can't encourage people who like your items to make an offer. Someone either will make an offer and buy it, or they won't.
Not a massive fan of VC tbh, awful customer service on VC's part. I also loathe when sellers send me offers for their items after I have liked something.
Occasionally, I have offered a price and it has been accepted. However, I haven't purchased it. Why? Either shipping and taxes (if it's overseas) has made the item more expansive than I realised, or simply, I have decided against the item for whatever reason. Remember, making an offer (and it being accepted) isn't binding, so the potential buyer is not obligated to buy.
Ultimately, an item is only worth what someone will pay for it. Fine if you don't need the money and are happy to have items for sale for years - I have items on my VC like list that have been there since VC started, and still the sellers haven't reduced their prices.
If you are a motivated seller, then price the item as competitively as possible and with the knowledge that potential buyers will offer 30% less of that price. Or else don't accept offers, many sellers don't, and just list a purchase price.