I'm going to leave this here, based on a comment you wrote underneath Mafii's answer:
+1 .. I like this way, the problem I am new here and my german is not good yet, that is why I didn't think about something like that link
If your German isn't that good yet, you are probably still struggling with your Basic Interpersonal Communicative Skills, BICS for short.
I've worked retail for several years, in the Netherlands (I also shop for clothes regularly). Over those years, I've met people that are just learning Dutch, or for who English is a second language. Sometimes, their response seems to suggest that they didn't really understand my question, because it didn't really make sense as a reply to the question, or they spoke so soft and accented that I couldn't really understand them. These things often led me to repeat my question, just to make sure the customer understood what I was asking, and I understood correctly what the customer was replying. I'd say in a little over half the cases, the asking again was 'correct', in that I either misunderstood the customer, or the customer misunderstood me. So, the clerk may not just be asking because they get a bonus if they sell you something, they may have just not understood you correctly or want to make sure you understood them.
Besided the sentences that Daniel and Mafii suggested (which do seem like correct ways to tell store clerks you're just browsing), try to mind your body language as well. I often let that help me decide whether or not to ask again when dealing with non-native speakers. Try to look confident when replying, and also when browsing the clothes. If you do take some time to decide, try not to look too confused. Stand up straight, focus on the product you're deciding about (maybe hold it in front of you and go look in a mirror, for example) or keep browsing the rack, speak with a confident voice (not too loud, but articulated and certainly not too soft either), make eye contact when speaking.
You'll probably notice that once your BICS improve, you're able to react and understand the store clerks better, but even then your body language will still play a role in keeping them at bay.