Depends on the context of the "advertisement".
A forum post is really related to the date that the item was posted.
I would not take any price I found here as gospel, but instead would go to the developer's site and review the price (with options included) and any other T&C's that relate to the actual purchase. They may charge for support or updates and that wouldn't necessarily be factored into the price, but certainly would be part of the cost of ownership.
You can't rely on any info in a 1yr old posting to be valid. Note that the version of cs-cart has probably changed 5 times since the original post.
Note too that places like the cs-cart marketplace do not account for product options that may modify the price. So what you see there may only be accurate for one set of option modifiers. I.e. I sell addons for V4 and MVE at a different price than the base price listed which is for V2.
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