Unless you have clearly explained your role to them it is possible they will assume that your role equates directly with the role of a teacher in their society. This may be different to here in Australia. The level of language required to operate at an acceptable level of politeness in a society is very high. You are misunderstanding their answers. A student has given me a gift.
Students giving teachers gifts in some societies is very common.
It is a way of showing appreciation for the efforts that the teacher has put in helping the student. It is very unlikely they are trying to buy a pass. Accept the gift with grace. It stands to reason that assignment work will be better because students have more time and more avenues of assistance in the completion of assignments. A well planned assessment program using a variety of assessment methods will limit this problem.