This is from Bhikkhu Pesala:
"As the Sayādaw points out, there are skilful ways to criticise the wrong conduct of shameless monks without making unwholesome kamma. Wise lay people can make merit by donating allowable requisites and paying respect to shameless monks. If asked for unallowable things, they can politely ask, “Is this allowable?” to remind a shameless monk of his remissness without criticising him directly. There are so many rules to observe, that even the most scrupulous monk is likely to overlook some offences. A lay person can give money to a lay attendant, inviting a monk to ask for whatever he needs. If a lay person gives money or other unallowable things to a monk, he or she will make only demerit.1 An attendant is living in dependence on the monk, so he should obey the monk’s instructions, but a lay person does not have to.
1 The word “āsādeti” means “invite to accept” or “offer”, so a lay person makes demerit even if a scrupulous monk refuses to accept money. Though the action of giving is incomplete, the action of offering is complete. Any honest person will be insulted if offered a bribe, and one can be arrested and charged with trying to bribe a police officer or customs official. Offering money to a monk is also an insult.
“Yampi so Tathāgatam vā Tathāgatasāvakam vā ākappiyena āsādeti,
iminā pañcamena thānena bahum apuññam pasavati.”
“Also, whoever offers to the Tathāgata or to the Tathāgata’s disciple what is not allowable, in this fifth case makes much demerit.”
(Jīvaka Sutta, M. i. 369)
Most Buddhists know that money is not allowable for monks, so why do they offer it? It is better to ask monks what they need. Even if the monk says that he does not need anything at the moment, one makes a great deal of merit by offering what is allowable, because the action of offering is completed. If one is determined to give something, one can give some money to a trusted lay supporter, and invite the monk to ask for whatever he needs up to the amount that one has given: “Venerable sir, I will give £20 to so-and-so, please ask him for whatever you need.”
To avoid being embarrassed by a greedy monk asking for too much, one can specify the value of what one wishes to offer — “Venerable sir, I have twenty pounds. Is there anything that you need?” If a shameless monk then asks for something costing £100, one can say, “I don’t think that can be got for £20, but I will try to find one.” Then the monk will get what he deserves, and the donor will keep his £20."
(from a Manual of Dhamma by Bhikkhu Pesala http://www.aimwell.org/Books/Ledi/Dhamm ... eword.html