We purchased master resell rights, from a reputable vendor, for a whole package of stuff, which included this particular product.
This is a direct quote from the "thank you" page, above the link we get the original "Congratulations, You now Own the Master Resale Rights to..." (followed by a list of software including the autoresponder unlimited zip file.
In fact, I would need to check, but I believe we may even have master resell rights to this package from more than one vendor.
In general, "Resell Rights" means that the purchaser (in this case us), can resell it.
In general, "Master Resell Rights" means that the purchaser (in this case us), can resell the product with resell rights included. So the purchaser's customers (in this case, you), also can resell the product.
In general, what is sometimes not clear with Master Resell Rights is whether the purchaser's customers' (i.e. you) get master resell rights (i.e. so your customers can then resell the script), or just resell rights (so you can sell the script to your customers and then they can use it but not resell it).
In general, what is also not always clear is whether the package can be altered or added too, e.g. can we add a better explanation to the readme and re-zip the contents.
I also did some quick checking
1. The original developer's site says they have sold the resell rights and master rights to this program (they are now doing something else)
2. Quite a number of sites offer packages including this product with master resell rights.
Based on this and the content of the package, it is my *belief*
(a) You do have resell rights, i.e. you can offer the script to your customers
(b) You *probably* do have master resell rights, i.e. your customers can themselves resell the script. This matches the overall packaging of the product.
(c) The text in other files "contradicting" the readme, applies to the original version of this script predating the institution of this reseller rights distribution, presumably when the vendor sold it directly to customers.
(d) It would probably not be wise to alter the script or package, without explicit permission, when distributing (the product itself gives you permission to alter it on your own site I believe). This is a slightly different issue from (a) to (c). as this involves preparation of a derivative work (something which requires permission of the copyright holder), rather than distribution (a different something which requires permission of the copyright holder).
It wasn't aware of this lack clarity in the documentation previously, thank you for bring it up.
Hold off distributing for a couple of days, and I will get a definitive answer.
If it in anyway turns out got less than you wanted/expected/were-told (even in a minor way), I will refund or give you a freebie (your choice, although there may be some restrictions on choices of applicable freebies) to make it up to you.