Occasionally, the antiexploit system gives some false alerts. For example, it used to ban GMs who were using the GMShop, thinking it's a non-gm char exploiting. Similarly, I have had some trusted players getting kicked/banned in the past. I know they hadn't tried anything illegal, but the anti-exploit punished them anyway.
However, for the most part the antiexploit system works properly. A proper client should always send the correct info when buying from a package-sale. For the info to be incorrect, it pretty much means that there is some kind of hack involved. This would usually mean either that the player is using a bot or a packet editor.
I personally trust the antiexploit system to a high degree...but you should be willing to talk with your players and resolve any possible misunderstandings
[22 Apr 19:47:31] AUDIT:Warning!! Character Bolsy of account denjoje tried to purchase over 2147483647 adena worth of goods., player Bolsy, 4
There are some limitations in the client. Namely, no number can ever be negative and no number can ever be larger than a certain value. This value is either 65,535 or 268,435,455 depending on the item (there may be some exceptions...not sure). In general, numbers that are larger than these values are also interpreted as negative.
Things normally get really wierd when the client attempts to use negative (or very large positive) numbers. In the past there existed a lot of exploits due to such values. Some of them include immortality bugs (players somehow managing to make their maxHP negative), trade exploits (players purchasing items for -1 adena) etc.
In order to avoid such exploits and make up for the client's limitted handling of these errors, anti-exploit code has been added in the system. If a player buys items of total cost larger than the maximum number that is properly recognized by the client, the server does not allow the trade to happen and produces the log entry you quoted.
This some times means that the player knowingly attempted to use an exploit and earn free items. Sometimes, it just means that the player mistyped or otherwise made an honest mistake. Again, this is a valid anti-exploit protection, but you should best talk with your player and see what he/she was trying to do...