Can someone purchase your script, change all the graphics that give credit to you, including the logo, and use it on a client’s website?
Ok I took a look at the ‘license terms’ and it didn’t provide a clear answer.
The meat of your question deals with ‘Attribution rights’. While the envato license makes no mention of this right some nation’s laws have ‘Attribution’ as an indelible right. In most places tough, including the United States you can sell attribution.
Unless there is a more detailed copy of the license hidden somewhere in the envato network the answer is that no, you cannot re-attribute the work.
I reason this because licenses are exclusive, you only ever have the rights that the license or other laws give you. Since the envato license does not give re-attribution then you are not purchasing said right.
If your talking about a standard license , I am almost 99% sure they can, but they may only use it once (ie they can’t put it on 5 client websites)