Doubt after completing Tawaf in the amount of rounds or in conditions of Tawaf like performing ablution or other acts correctly, should be ignored.
Whenever a pilgrim has doubt after reaching al-Hajar Al-Aswad that did he/she perform seven rounds or eight rounds or more, he/she should ignore that doubt and Tawaf is correct; also if during the rounds he/she has doubt that if this is the seventh or eighth round or more than that, this doubt should be ignored and after finishing that round Tawaf is correct.
Whenever a pilgrim doubts about performing less than an amount in obligatory Tawaf (like the doubt between six and seven or five and six etc.) it is obligatory precaution to leave that Tawaf and restart if from the beginning (this is for obligatory Tawaf), but in Mustahab Tawaf he/she can consider it as the lesser number and Tawaf is correct.
Assumption and guessing is the same as doubt in past issues and should be acted as the rulings of doubt.
There is no problem in relying on a friend for counting the rounds of Tawaf (if that person is a reliable person).
A doubtful person (a person who has lots of doubts in Tawaf) should ignore his/her doubts, and take the number which is more appropriate for him/her, for example this person should take six between five and six, and take seven between seven and eight.
Talking, laughing and even eating something do not invalidate Tawaf, but it is better not to say a thing other than prayers to Allah (in Mustahab or obligatory Tawaf) and to perform this great worship with presence of the heart and abstain from doing anything that reduces presence of the heart.