In the following case, why would it have been better if the police sent only the three radios stolen earlier instead of adding more? Police...

It would have been better if the police had only sent the
three radios with the thief because then there would be less ground for the defendant to
claim entrapment.

Entrapment occurs, as the link below
says,when government officials do something

readability="5">

that induces a person to commit a crime he or she
is not previously disposed to
commit.

One can argue that
the defendant was previously disposed to commit the crime of buying the three stolen
radios, but that he was not disposed to buy the other 11 that the police sent along with
the thief.  Therefore, by sending the extra radios, the police actually bolster the
defendant's ability to claim entrapment.

The defendant can
also claim that the other 11 radios were not actually stolen property.  He can say that,
once the police got possession of those radios, the radios ceased to be stolen
property.

It is not clear that either of these defenses
will work, but they were made much more feasible by the police action in adding the 11
other stolen radios to the original 3 the defendant was going to
buy.