awk to compare lines of two files and print out screen

hey guys, I have two files both with two columns, I have already created an 
awk code to ignore certain lines (e.g lines that start with 963) as they wou
ld begin with a certain string, however, the rest I have added together and 
calculated the average.

At the moment the code also displays the two files in one list showing just 
the lines it used to calculate the average. 

e.g
FILE1
812353124 54
812535352 55
864235235 99
963352351 35

FILE2 
812353124 75
815342325 93
864235235 52
963546253 46

***
output on screen
812353124 54
812535352 55
864235235 99
812353124 75
815342325 93
864235235 52

Average: <number calculated>
***

What I want to do now though is to compare each line on both files, and if t
he first column of a line matches one in the second file, it will print a th
ird column with that file. If one line doesn't match in the other file, the 
third column will have a * on that line. 

Example of output

812353124 54 75
812535352 55 *
864235235 99 52
812353124 75 *
815342325 93 *

as you can see, there are no doubles of lines that match in the first column
.