Style expressing pronouns

böylesi --> something/somebody like this.

öylesi  ---> something /somebody like that.

böyleleri  ---> the ones like these.

şöyleleri  ---> the ones like those.

Böylesi zor bulunur.--> It is hard to find something/somebody like this .

Öylesine güvenmeyeceksin ---> One should not trust somebody like that.

Böyleleriyle fazla samimi olmayacaksın ---> One should not be very close with people like these.

Şöyleleri  ham karpuzdur. ---> Watermelons like those ones are not mature [ready] yet.

In the last example how is the negative--not-- translated?

I think the more literal translation of the last sentence is:

Şöyleleri  ham karpuzdur

The ones like this are green (immature) watermelons.

So in this sentence there is no negation - there is only statement that the mentioned things are immature watermelons. I think that Tunci simply preferred to translate this sentence using negation.

Yes , as Tomac said, I preferred to translate that sentence using negation. 

"ham " can be used for fruits which are not ready . [ not mature = immature]