Problem with Roman Empire coins Pricing

[ducnguyen]

I just bought 2 Roman Empire coins recently: Roman Empire Diocletian and Roman Empire Constantine I
But I have 2 questions which I could not find the answer through websites:
     1) The Roman Empire Diocletian coin is graded AU (Almost Uncirculated) by NGC although its surface is quite bad. If we look closely, we can easily see the roughness caused by a long-lasting oxidation reaction. On the other hand, the Roman Empire Constantine I coin is more beautiful than the first one but still in the same grade. So which coin is evaluated accurately?
     
     2) According to you guys, $53 for the Roman Empire Constantine I coin is a good or bad price? Is $67 for the Roman Empire Diocletian coin suitable?

Link: http://www.ebay.com/itm/Roman-Empire-Diocletian-AD-284-305-Bl-Nummus-8-36g-Trier-Genius-NGC-AU-Silvering-/352046314589.
         http://www.ebay.com/itm/Roman-Empire-Constantine-I-AD-307-337-AE3-Bl-Nummus-NGC-Ancients-AU-/371930653310
       
 Thank you.

[Victor]

you will almost always pay more for a coin in an NGC slab, but having said that, the prices you paid were not bad.

NGC charges $25 to encapsulate ancient coins, so subtract that from what you paid. So you got the Constantine for under $30, and the Diocletian for around $40, which once again, is not bad.

[ducnguyen]

What are the cheapest prices these two can be? I am learning how to deal with prices.

[Victor]

Prices vary according to many different factors. I sold a Constantine I campgate from Cyzicus on eBay for $14.50. Yours is nicer...is it that much nicer? You have to decide these things for yourself.

A good way to figure out what coins are worth is to watch a lot of auctions. You will eventually have an idea of what some coins sell for...so pricing ancients is based largely on experience.

The pricing of ancient coins is very subjective and not at all like US coins which have price guides based on an elaborate grading system.

[ducnguyen]

Do you agree with me that the Constantine I coin is better than the Diocletian one? The only reason that I paid more for the Diocletian coin because it is larger. But the NGC still grade them the same??? Or maybe when we clean, the Diocletian will look better? I never believe that $14 can buy anything which a part of history.
When I bid an item, I will look up for the similar item's price and calculate the difference. I am sure the prices that I paid for them are lowest on that auction channel base on the quality compare to price. But there are some channels still sell things cheaper than what I have researched. For example, you sold the similar coin with no slab for $14 on eBay. Nah, I never though about. The last time when I bought the Aurelian coin for $200 with no slab, at that time I though it was already cheap (not the cheapest).It had already be discounted( the original price was $1000) But you told me that they should sell me for $75. I thinks my coin's face is better. That made its value, it looks smoother than scan picture. I even still though it look like an uncirculated coin. Then I find a few coins in the same situation but been graded almost uncirculated. There are many coin look worse and got mint state grade by NGC. I don't know what to believe.

[Victor]

I never believe that $14 can buy anything which a part of history.

You can actually get a lot of great deals if you know where to look.

For instance (shameless plug), I list a few coins every week on eBay starting at .99 cents with free shipping in the USA.

http://www.ebay.com/usr/victor_clark