Someone who is genuine in their collecting will be grateful for whatever is given.
Whilst one should strive never to refuse the giving of tzedokoh (I don’t want to get into the halachos here) at the same turn, a person genuine in their collecting may not refuse what is given to him. If the amount proffered is rebuffed one may decline to give the person anything.
I know times are hard but most collectors are genuine and only a small minority are a bunch of crooks who spoil the name for the many good people who come collecting either for their familiy or a good cause.
As for people coming after ten o’clock. Please remember men often come round after Maariv which can well be after 10 o’ clock. They are also charged per hour and / or by the day by their drivers and so want to cram in as much as possible during their short time in your locality with as many as can fit into one car. Therefore it is always a good idea to divide your donations so there is a spread.
If you give over a certain amount your house is marked by the driver for future meshaluchim who will come in droves demanding a high figure.
Sounds all a bit mercenary doesn’t it and makes you very sceptical but that’s how it goes.