Is every IIM give the gurantee of placement.
According to statistics every IIM complete 100% placement every year though quality of placement do vary from college to college. Don't focus only on average or median package because it varies a lot between the highest and lowest package. But yeah one thing you could be sure about 100% placement in IIMs because placement committee keeps on calling companies till the 100% placement is not done. Although quality of companies degraded data by day and package Offered also decreases. The better IIM in you are better will be the distribution of packages among all students.
No IIM guarantees placements. It totally depends on how you perform. However the placement committees at most IIMs are able to place the entire batch and achieve 100% placements. There are a lot of companies visiting IIMs and you have ample opportunity to get into one.
Students are allowed to appear for the placements if they fulfill the minimum criteria. However no IIMs give the guarantee of the placements. You have enough opportunities to get selected in your dream companies.