There are three types of stat bonuses on equipment: Hardcoded, Modifier, Random
Take a look at this example item with the following stats:
Grand Senior Look
[Max HP 136] - Hardcoded stat bonus
[Max HP 158] - Modifier stat bonus
[Strength 5] - Random stat bonus
1) Hardcoded stats are stats that are ALWAYS on that particular item. Not every item has a hardcoded stat. They are the first (highest) stat you will see on the list. Senior Looks have a hardcoded Max HP 136. Every Senior Look, Blue or yellow, crafted or dropped by monster, will have Max HP 136 at the top of the list.
2) Blue Items have a modifier stat. This will be the next lowest stat on the list. As someone already posted somewhere:
Demon = Critical
Dark = Attack Speed
Grand = HP
Golden = MP
Elven = MP Rec
Legend = Dex
Demon, Dark, Grand, Golden, Elven, and Legend items are all usable 5 levels earlier than their yellow counterparts. Saint items recieve no bonus other than they are available 10 levels earlier than its yellow counterpart.
Grand items always have a HP bonus. The higher level the item, the more HP, but it is always the same for THAT particular item. A Senior Look that is Grand will always have Max HP 158.
3) And finally, sometimes items have a random stat (or more than one random stat). This is where crafters get lucky (or try to =). Each of those has a max. This is the max that people have been asking about, but the two other types of stats (Hardcoded and Modifier) are not subject to the max limit of the random stats. As someone already posted somewhere:
+20 charm
+6 for the other 5 basic stats (STR, INT, DEX, CON, SEN)
+14 critical
+8 attack speed
+6 movement speed
+10 dodge
+10 defense
+40 max MP
+40 max HP
+10 attack power
+10 accuracy
Note that you can recieve the more than one random stat on an item. You could get 8 Accuracy and 6 Attack Speed as random stats on a single item. For example, someone posted they got a weapon with CRIT 14, and then again CRIT 14! Obviously, that's ideal for a character built around doing critical hits. I have even seen an item with AP (Attack Power) 5, and AP 2, for a total bonus AP of 7.
However, apparently some multiple random stats influence each other. Example: Many people look for AP 7 / STR 3 masks. The reason is there are no AP 10 / STR 6 items. I believe this is because some characters would actually get more than 10 AP from an item like that (when you include the AP recieved for the STR bonus). So, I believe the game designers set up rules so that no single item could give more than 10 points of AP.
Well, I hope this explains a little. If I'm wrong about any of the numbers feel free to post it here. However, please only do that if you have actually seen the items stats. Also, be warned that there may be some rare super-powered items in the game that were hacked in before they got security tightened up. Example, someone said they saw an AP 15 item in a store. That item was not legally created in the game.