OP, I was coming on here to see if you could find a forum where you could get opinions from posters who've lived or worked in Tunisia rather than just gone on a package holiday there for 10 days, and maybe not seen the best of the country. So this post by Aichek is great! Listen to her, not to people who've been to a resort for a week.
If you repeat the same old tourist well-trodden paths, then I'd imagine you'll replicate some of the same old experiences. So yes, expect hassle aimed at perceived wealthy Western tourists with money to spend in the obvious places. Who else are souk traders going to sell carpets, brass wear, leather etc to if not to hordes of tourists who want something 'authentic'? I bet the local consumers of such goods have long since deserted the heaving souks and prefer their own outlets - or reject those things entirely because they're 'old fashioned'.
Just be sensible. It's a Muslim country, so dress conservatively and respect local customs. Whatever you consider 'covering' clothing, I'd dial up a notch or two - so if you'd happily wear shorts or a shorter dress at home in the UK, I'd go for long trousers or a longer dress with sleeves or a wrap. Late June is going to be SO hot though!
I'd strongly consider hiring a guide and going away from the main touristy areas - get a guide who can take you to some amazing Roman archaeological sites. Having a guide will also protect you from an awful lot of the hassle and touting. Don't forget to visit museums, you'll see some of the best mosaics you can find, and they may well be nice and cool in there.