I'm thinking about selling my iphone?

I reset my iphone and all my data has been deleted, but I'm still paranoid that the person who I'm selling it might recover my data. I had some personal information and pictures that I wouldn't like a stranger to see.So, is there a way to make sure that they won't be able to recover anything? I'm not selling it to a friend or anybody I know, more like a shop where you sell used electronics for money.

If you fully restored the phone you have nothing to worry about.