@LoobyLou1976
Must admit, it is strange to just knock on someone's door rather than go through the estate agent. But people do!
I wouldn't worry if it IS someone trying to take stuff from your skip... When we moved house last (several years go,) we had a 'mini' skip (because it was sooooo expensive for a 'midi and a 'large.')
We filled it up within about an hour, and we were miffed because we had loads of stuff/rubbish left! Like we needed another 2 bloody mini skips worth.
Cue the travelling folk! Tap, tap, tap on our door. 'May we take some of the stuff out of your skip?' I said 'knock yourself out mate!' 
They virtually emptied it. I thought it was just tat in there (old broken toys, gadgets, ornaments, and old pictures/picture frames, pieces of chipboard and wood, and a couple of broken electrical items, as well as old knackered clothes and shoes not fit for the charity shop.)
Because of that, we were able to fill the mini skip again, (as they emptied out 65-70% of what was in there.)
Then they came back a couple of days later, knocked on our door and asked again if they could have a mooch through our skip. We said yes. A couple of days later, they took a load more stuff out of it again... (for a third time.) Sooooo we had room for even more stuff.
By the time the skip folk came to get it, it was only half full!