I have a Firearms Dealer license and want to sell guns online.  I need
to know the following:

1.  What are the most frequently used web sites to sell firearms? I
know of gunsamerica and auctionarms.  What are the other big ones and
which have the most guns sold on a regular basis (I don't want to list
on a dead site)?

2.  What are the most frequently BID UPON guns on these sites?  I'm
not interested in what guns are listed often, but those which actually
sell, or at least which have people bidding on them even if they don't
make the reserve.

To clarify question 2, I will add:
A. I am only going to sell new, unused firarms.  Not interested to
know that used Glocks are hot, etc...
B. I am interested mostly in pistols, but also want some info on
rifles and shotguns. I prefer to deal with the
military/police/self-defense market, since I am unfamiliar with
hunting weapons like .270 rifles or trap-shooting bird guns, etc...
C. There needs to be at least a LITTLE detail, but not minute details.
 For example, an answer of "AR-15 style rifles" is not enough.  I
would need to know the brand. An answer like "Rock River AR-15-style
rifles under $1000" would thrill me, as would "Glocks in .40 cal". 
But "Rock River Government Model with two-stage trigger, 4-way
collapsable stock  and hogue grips with EOTech 552 Holo sight in .223
caliber" would be overkill, as would even "Glock Model 23C with
Trijicon adjustable night sights"

I would be very pleased to find at least 10 handguns and at least 5
each of rifles and shotguns in your answer.

NOTE: This is my first use of Google Answers.  If my pricing is
inappropriate, please let me know.  I only get online about every
other day so it will take a while for me to respond.  Thanks!

I gave it my best shot!  (no pun intended)

I searched various styles of styles and calibers of pistols to and
looked through the results to see which manufacturer seemed to have
the most bidding activity.  I then narrowed down my searches to an
individual manufacturer and then to caliber or model each time trying
to find which was being bid on the most.  The results below reflect
those specific firearms that seemed to have the most bidding activity.

My search criteria was only ?Modern Firearms? ?Factory New? and sorted
by ?Highest Number of Bids?

These results are from gunbroker.com.  The number for each firearm is
the number that variety (factory new) that currently is being bid on. 
They have not necessary reached the reserve price yet.

Pistols:

17 ? Sig Sauer 9mm (models P226, 228, 229) ? 17 bidding, mostly in the
$300 ? $500 range but as high as $1800

17 - S&W 38cal.  Revolvers (various models) ? 17 Bidding, prices
anywhere from $200 to $1000  Mostly in the $300 range

14 - Beretta 92fs ? 14 bidding under $500

13 - Springfield 1911 ? 13 bidding from $250 to $1100

13 - Colt 1911 ? 13 ? Most around the $500 to $800 range

11 - Glock 9mm (models 19 and 17) ? 11 bidding under $500

7 - Springfield XD-40 ? 7 bidding from $300 to $400

7 - Taurus 38cal Revolvers (mod. 83 ? 85) ? 7 bidding between $100 and $250

7 - Glock 40cal (Mod 22) ? 5 bidding under $500

When you?re talking handgun, 9mm is still the most popular caliber. 
That?s why the Sig p22x, Beretta 92fs, and the Glock 17 and 19?s get
so many bids.  The most popular revolver round seemed to the 38 cal. 
I am hoping that by putting the price points that I saw it will help
you decide which guns might be profitable to sell.


Rifles:

27 - Winchester Mod. 70 ? (various calibers) ? 27 bidding mostly
between  $300 and $900

19 - Remington 700 ? (various calibers) ? 19 bidding mostly between $300 and $700

5 - Bushmaster AR-15 ? 5 bidding between $200 and $700

4 - rock river AR15 ? 4 bidding between $450 and $700

3 - Colt AR15 ? 3 bidding $630 ? $1300

Rifles are much more difficult.  I tried to stick to military type. 
These are two basic types of military rifles, assault and sniper. 
These are some of the most popular.


Shotguns:

8 - Mossberg 500 12GA ? 8 bidding between $100 and $250
8 - Remington 870 12GA - 8 bidding between $150 and $350

These are the two most popular defense/assault shotguns.  I looked for
more that seemed ?popular?, but couldn?t find one that was close to
these two.  Winchester 1300 was the closest.

I hope that this information helps.  I went ahead and posted this as
an answer.  If you find the information is not what you are looking
for or is insufficient please let me know and I will do some more
searching.

I?ve thoroughly enjoyed researching this for you.
 
Thanks!

This was a tough one.  Thanks for checking it out for me and for being
so friendly.  Well done!

GunBroker.com is the largest online auction house for firearms.  I
just checked their listing and they have more than 22,000 items listed
under their "Modern Firearms" category.  Although I do know that some
of the listing under that category are things like barrels.  I've
purchased several firearms from here.  They are going to be your best
resource for selling firearms.

AuctionArms.com is an auction competitor of gunbroker and not nearly
as large.  They have about 5500 items listed under "firearms" right
now.

GunsAmerica.com is the largest gun classified site that I was able to
find.  It is nearly impossible to determine how many firearms are
listed, much less sold through that site.

I've been working on searching through the sold archives of both of
the auction sites listed above to develop your list.  It is not an
easy task.

The mentality of someone purchasing a firearm on these auctions sites
is that of a bargain hunter.  A person can go to their local sporting
goods store and hold or even try out different firearms to compare
their features.  If they are looking online it is for something they
can't find elsewhere, or they are looking for a bargain. Usually the
latter.

As I've looked at what guns are selling, it?s hard to nail down models
or even brands that sell better than others.  It comes down to price. 
A good deal on any make or model of firearm is going to sell.

I am going to continue to research this for you (mostly because I love
looking at firearms, even if I don't have the money to buy the ones I
want right now), but I'm not confident that I will be able to come up
with the answer you are looking for.  Thanks for your patience while I
work at this.

I'll let you know what I find either way.

Thanks for giving Google Answers a try!  I hope I can help you out.

Well, thanks for the help so far!  If you don't get to it, no big
deal.  If you do, a nice tip is coming your way.

As for bargains, that's fine.  I have access to wholesale prices, and
don't desire to mark 'em up a whole lot.

I may just do a little trial and error.  It's mostly for a hobby and
supplemental income.  Not like my mortgage depends on it... :)

Thanks, Luke