There are legitimate reasons for such delays, although it seems a lot of people have been claiming these things are happening to them. Unless you have proof to the contrary, you have to accept their word about what happened.
A number of other scenarios are possible, but I hate to dwell on the negatives.
If no other options are available to you besides posting negative feedback, you lose nothing (unless there's something you haven't mentioned) by waiting. You can always post it, but if there turns out to be a valid reason for the delay, you could have to make an embarrassing public apology if you post negative feedback early.
6 days/1 week delays have happened to me also, as both buyer and seller. It made me very edgy and all kinds of bad thoughts went through my head. Balls were eventually bought and sold.
Good luck.
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