The first question to ask is how long has it been since you contacted them? Off the top of my head I think there is a time limit for a store to respond (it might be 48 hours, but don't quote me on that), so if it's within that they may still respond.
Also a lot of sellers have other commitments, be they family or other jobs, that may impact on how soon they can respond, or a sudden emergency or technical issues that could delay a response. I would still expect a brief message to at least say they've received your query.
However, if it's been some time and you haven't heard anything I would send another message, and also contact site admin (link at the bottom of the page), explaining the situation.
If the seller hasn't responded after a few days, go to the order, click on 'More Actions' and then 'Report an issue' That will alert the seller (again) not only with a message, but also a banner on the site (I think every page) and also gets the attention of Admin, no need to e-mail the admin
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Also a lot of sellers have other commitments, be they family or other jobs, that may impact on how soon they can respond, or a sudden emergency or technical issues that could delay a response. I would still expect a brief message to at least say they've received your query.
However, if it's been some time and you haven't heard anything I would send another message, and also contact site admin (link at the bottom of the page), explaining the situation.
Hope this helps.
That will alert the seller (again) not only with a message, but also a banner on the site (I think every page) and also gets the attention of Admin, no need to e-mail the admin