I'm new to italki and have never chatted with anyone here via Skype, but I've used Skype many times and found it to be safe.  Keep in mind, too, that you can keep the camera/video turned off and just use the audio.  :)  You'll miss out on nonverbal communication but it might make you feel more comfortable!  You could keep the camera off for the first, say, five minutes or more...just tell your chat partner your camera isn't working.  :) Once you decide they're not a creep or pervert, you could then say, "oh wow! My camera works!"
Not that I've ever done any of this!!  ;)  But if someone is looking for something other than conversation practice, you'll usually figure it out right away.

Buena suerte!

What harm could happen during a skype call?

Make the call, if your language partner is a weirdo or does something inappropriate, just end the call, click block and come hee in order to find more as if nothing had happened! 

But if you want to be more secure about your the real intentions of language partner, ask questions about how he or she would like to do the language exchange and see if his or her profile is accordingly. 

I have never had a bad experience using Skype to talk to Italians in Italy. It is a great way to improve your conversational ability. Of course, some people are more helpful than others, and you will find that you get along and find more to talk about with some than you may with some others.

Regarding safety, I don't see any way that you can be harmed through a Skype call even if you happen to encounter a nut. Perhaps you may be offended, or disgusted, but that can happen anywhere. To be safe, however, I would suggest that you not give out information that would allow a person to come in physical contact with you. For example, don't give out your home address, or work address, or home phone number.

Of course, once you get to know someone fairly well, you may decide to be more open. Meeting someone on Skype is no different than meeting a person in a classroom situation, and the same freedoms and cautions apply.

Some women encounter perverts who offer them to video chat but when they turn on their cams they do nasty things. Keep in mind that Skype links one's Facebook and Whatsapp acounts to one's Skype account. So, if you want to keep your privacy create a new Skype account only for adding people to practice Spanish with.

I think all previous comments are right. Just be on Skype as careful as you are on your real life: give an opportunity to anyone who wants be in contact with you, but don't share your personal details in your first encounter. And block them if they show an inapropiate behaviour: in fact, this is much easier to do in Skype than in real life.

@Jessica: currently, I have five partners with weekly encounters. I am male, and all of them are female. What if they had banned me, only for be a man? I think is a bit unfair. We are all learners, in spite of our gender. I sent and received lot of messages  asking for exchanges, and tried a big part of them, but eventually I only succeeded with these five partners. The fact they are women is not important. I understand your concerns, but you can protect yourself easily with some simple rules: start your interchanges only messaging on Italki. If your partner shows as a reliable person, you can switch to text messaging on Skype. Also, you can take a look to his profile and survey his previous activity correcting notebooks, or taking part in discussions. It's easy to know who is really interested in learning, and who is a casual user in the community.

Really, I don't know any woman here in Italki who told about  a real bad experience. Sometimes it sounds like an urban legend: "I have a friend who knows a person who tells him that he knows a girl who..."

Be careful, but don't be unnecesarily afraid.