Hi Preeti,
i will never ever suggest you to go with any unauthorised sap training center, the reason behind is that
firstly they will provide you training for that and the content of their study materials are not authenticated, and hence will not be acceptable by means of understanding the concepts of that module. Second thing is in concern to sap which is already discussed by previous post.
Now , can i know the purpose of taking certification because if you are a working proffessional then your company may help you in taking your certifications, but if you are not working, then i am not seeing any positive thing apart from boosting your resume because taking a certification never gurantees a job in sap field.