The answer would depend on what is considered acceptable in the community where you are collecting.
If the average collector got e.g. 25% than you would have to inform the giver if you were to take more. If the prevailing attitude is that any percentage is OK as long as it meets the requirements described in the link you provided than that would be OK too.
For any deviation from accepted practices you would need to inform the person giving.
If you collected from someone who was totally unaware that collectors receive any commission there would be no need to inform the giver that you are indeed taking a cut.
Again this all assumes the collector is acting within accepted norms of the community where he is currently collecting.
Shulchan Aruch rules (Choshen Mishpat 228), it is forbidden to
give others a wrong impression, the more so where there is a monetary
ramification. This falls under the prohibition of geneivas daas,
“stealing another’s heart.”
The Shulchan Aruch rules that where a person acts in a normal way, yet
somebody else receives a wrong impression, there is no obligation to
correct the wrong impression. Only where a person actually creates the
wrong impression does he trangress the prohibition.