Someone wants to buy one of my rifles and they will happen to be on Oahu this weekend but they are a resident of Maui. Usually when I do face to face sales I ask for their HPD Permit to Acquire. I'm guessing Maui county has a permit to acquire as well? Is it just the same procedure with me giving HPD the bill of sale/notification of sale after the transaction and they would go and register it with Maui police?

You should still require that the buyer provide a copy of the permit to check the dates and make sure it's valid.  It wouldn't hurt to take pictures on your phone of the original permit, the buyer's photo ID, and of the buyer.  Notify HPD of the transfer in writing within 2 days.

Hawaii County Police website has a transfer form letter that should work fine with appropriate changes for Honolulu PD references.

http://www.hawaiipolice.com/wp-content/uploads/2011/10/gun_transfer.pdf

You should give the buyer a copy of your HPD firearm registration, or at least the control number printed on it.  That assists the police departments when matching up the new registration and the old.  It also helps if the description of the firearm can be copied from your permit to avoid mistakes.

     In all cases where a rifle or shotgun is acquired from another person within the State, the person who is transferring title to the rifle or shotgun shall submit, within forty-eight hours after transferring the firearm,
to the authority which issued the permit to acquire, the following information, in writing:  name of the person who transferred the firearm, name of the person to whom the title to the firearm was transferred; names
of the manufacturer and importer; model; type of action; caliber or gauge; and serial number as applicable.

Only thing you have to do is notify HPD that you sold it, nothing more nothing less.

The law as seen below, dose not require you to check for ID, check for a permit or anything else. Only that you must let them know the name of the person. This is the name thet tell yout.

HRS 134-2 F
In all cases where a rifle or shotgun is acquired from another person within the State, the person who is transferring title to the rifle or shotgun shall submit, within forty-eight hours after transferring the firearm, to the authority which issued the permit to acquire, the following information, in writing:  name of the person who transferred the firearm, name of the person to whom the title to the firearm was transferred; names of the manufacturer and importer; model; type of action; caliber or gauge; and serial number as applicable.

It is made clear by the law that ID and verification of a permit it not required by the fact that it states for a pistol it is. This being true it clearly means it is not for a rifle.

hRS 134-2 F
     (f)  In all cases where a pistol or revolver is acquired from another person within the State, the permit shall be signed in ink by the person to whom title to the pistol or revolver is transferred and shall be delivered to the person who is transferring title to the firearm, who shall verify that the person to whom the firearm is to be transferred is the person named in the permit and enter on the permit in the space provided the following information:  name of the person to whom the title to the firearm was transferred; names of the manufacturer and importer; model; type of action; caliber or gauge; and serial number as applicable.  The person who is transferring title to the firearm shall sign the permit in ink and cause the permit to be delivered or sent by registered mail to the issuing authority within forty-eight hours after transferring the firearm.

If you follow the format of the form letter from the Hawaii County Police website I linked earlier, it'll help you collect and record the info the police will be looking for.

Going by the letter of the statute is one way to do it.  Using a little common sense means going above the bare minimum.