I think that you are wasting time over a non-issue. If a person inquires about a yo-yo and begins a negotiation that is great. They are under no obligation to continue or finish this negotiation. If they choose to stop negotiations - that is their business. Since you have no idea why they stopped the process you have no reason to feel bad, or dis-respected. It is anyone’s right to not-communicate. This is not rude, it is business.
As a caveat - you as the seller, are under no obligation to sell a yo-yo, at any price, until you agree to sell it. Yes, that did make sense. What I mean is that just because you are negotiating with one person - does not mean that you can not negotiate/sell to another person. Too many people have started a negotiation with: “Hey what about $50 for your mint Anglam?”. After telling them that this price is not acceptable you hear nothing. Two days after you ship to someone who is paying a reasonable price I get an email asking why I sold the Anglam “out from under them”?
Until a price has been agreed upon AND - note the stress here - AND they have paid me with cash or Paypal; that yo-yo is still for sale to anyone with the price I am asking. The first one with the money wins!