Hi
Sellers can block another member if they want to and they do not have to give a reason. Its their choice.
OR do you have 2 non payment strikes in the past 12 months? This would stop you from bidding or making an offer if the seller has their preferences set to block bids from anyone with two unpaid strikes.
Does the seller ship to your location? Again depending on their bidder preferences this would stop you from bidding.
