Bogus bidders

[valentineval14]

I'm new to selling. 2 out of the 3 items I've listed don't feel right... 

ITEM A - sold in auction for £63, a price I was happy with. Successful bidder never paid, so I cancelled the order and relisted it. The same person won the bidding the second time, at an over-inflated price of £400. I knew she had no intention of paying, and I was proved right!

ITEM B - sold as 'buy it now' for a price I was hPpy with. Buyer paid but never responded to my messages in trying to arrange the collection. 
What's is going on here? Is this usual practice? 
Also, I wanted to contact a previous bidder to see if they would be I terested, but can find no way to contact them. 
Ive tried to report these people, but there are no 'categories' on the drop down lists that fit the bill of these strange (to say the least) people. 
Interested to hear your thoughts and advice 

Thank you

[61stephenuk]

Read this announcement on how to cancel a sale and give bidders who don't pay an unpaid strike,2 or more strikes will stop them bidding from many sellers.You are in time still.

Then add their username to your blocked bidders list Here

Also Here to set bidder preferences and block bidders who have 2 strikes in 12 months

[valentineval14]

Thank you so much for taking the time to help with this. I’ve tried to block her, but her user name can’t be found. I guess she’s changed it so she can carry on playing silly games!

[plpmr]

adding to 61stephenuk advice -

When new to anything it's always best to read up on rules etc to protect yourself and the leaving of false positives for buyer's is serious feedback abuse that can damage your account.

[arkwebus]

Certainly looks very odd.  This may be malicious by the first bidder.  You can perhaps contact customer service through "help and contact" [top of pages]  to see if they feel that it is and they might do something.  

As to the fish tank collection items often present a problem.  "Regret" "too big to collect"  "too far away" and so on.  Just go through the "cancel/non payer" method which will give you a fee credit and the non-buyer a defect. 

Two defects and he will not be able to buy!

@valentineval14