The usual culprits on the Interarms guns are ammo and magazines and a good, thorough cleaning. And as No. 1 stated, running some rounds through it will help as well.
If you find that one brand of ammo doesn't work, try another and then another, if necessary, until you hit on one that properly cycles. I've found that Winchester White Box (when I can find it anymore) is just about foolproof in the Walthers; it always works fine in the two Interarms guns that I regularly shoot: one in .32, the other in .380.
Once you get past that, be sure to look to your mags for easy answers. Swap out one mag for another and see if you notice any difference in performance. Sometimes a simple adjustment or a new spring will do the trick and save you a lot of 'smith time and money.
Finally, be sure to give the gun a thorough cleaning, top to bottom and side to side, before you take it out the next time. Remember that's it's hardly new; who can say how it was treated before you got it?
Good luck.