How to handle this kind of person?

Go up to him, tell him that this is your set and that he kindly may stop playing samples in your set.
If he does not do it, go to the organiser tell them that this is not what you were hired for in a very kind way and that if it does not stop you feel unable to continue.
If he continues and the organisers do not do anything: Get your plan B playlist ready, put it on autoplay and go have a drink and be happy that you get payed for this bull***.
Always stay calm and polite.
If the organisers ask why you are having a drink and are not on the decks, simply tell them that he insists on playing and you are unable to stop him, so you let him have it.

I had an equally frustrating night as well. I got hired to play at a skate rink for the 11pm-1am adult skate. I was asked to play “JB Skate Music” which in Chicago means James Brown, 70’s Funk, R&B Soul music. I spent the week putting together sets from 80bpm – 110bpm which is a good skate tempo. A girl (who I thought was the promoter) kept coming up to me all night complaining about the music. It was as if she didnt know any of the tunes or we weren’t on the same page with JB Skate. Turns out she said to me after an hour; “When I say JB Skate I dont mean James Brown, I mean JB Skate music.” Seriously, she said this. I asked over and over the names of some groups or songs and she couldnt but kept showing me her iPhone play list. I didnt recognize anything. She brought a stack of 4-5 CD’s and asked me (while playing) if I could listen to the CDs and pull something off that. In the end I realized she listens to alot of her DJ friend mix CD’s and doesnt know song titles, names or anything. It got so frustrating that for the last 15 minutes I put in a CD and let it play. It was the DJ’s own production of beats with partial song loops. No wonder she didnt know anything – and it certainly wasnt James Brown.

That’s a rough one.. we all want to be diplomatic but there are times when we do have to take a firm stance. I had another DJ who used to always come up to me because “he had an idea” when I would have the dance floor hot and going. He always wanted to mix into my set and always wanted to play a song when things were going good. I had to tell him that he had his time and now it’s my time. Fortunately he didn’t take it too personally and even apologized for his actions. The best thing you can do is maintain your professionalism. Let the person who hired you know and if they don’t do anything about it, just simply choose not to play there again.