"Best friend" is the right approach. You absolutely would do things if your best friend asked you, that you would not do for a random charismatic stranger you just met at a bar ("Hey, can I hold your treasure while you go to the bathroom?" "OK!"). If you asked the ensorcelled person to do something which they would NOT do for their best friend ("Let's kill these orphans and take their toys!") it doesn't work. A charmed person is just so incredibly naive and nice toward you that you feel ashamed taking advantage of them, and they will really feel betrayed if you push them too far and break the spell. If you make a request which falls somewhere in the gray area, give the target another roll to refuse and/or break free of the enchantment.

One reason to avoid the more powerful interpretation of this spell is that it works both ways! You won't be laughing when a 1st level NPC Magic User destroys your entire party by casting Charm Person on the fighter.

Natural lycanthropes are usually born not made

The Monster Manual on Lycanthropes says

Sometimes a lycanthrope begins life as a normal humanoid or giant who subsequently contracts lycanthropy after being wounded by a lycanthrope. Such a creature is called an afflicted lycanthrope. Other lycanthropes are born as lycanthropes, and are known as natural lycanthropes. (MM 170)

Emphasis mine, but, of course, individual campaigns may vary.

Alternatively or in addition, a generous DM may allow a character to gain the template natural lycanthrope by undergoing a variant of the Ritual of Vitality (Savage Species 150).

Finally, the prestige class silverstar (Faiths and Pantheons 201-2) at level 6 gains the (presumably natural) ability Selûnite lycanthrope which says that

Upon reaching 6th level, silverstars who contract any form of lycanthropy are treated as natural lycanthropes. (202)

Whether a silverstar can pass on to its offspring this treated-as-natural lycanthropy goes unmentioned by the text. (The DM must make minor adjustments to the prestige class silverstar for compatibility with Dungeons and Dragons 3.5 anyway, so ask when he does.)