It is big dilema
I have some problems in the past with same problem so I will get some points.
1) NGC or PCGS do not grade cleaned or dipped coins ANACS will do prograde usually 2 grades lower
2) Recently I discover toning on my coin that looks like dipped coin I am send it to Apperance review.
3) Cleaned coins are usually do not have nay luster (some dipped coins have thanks for this information to BankNote1) or they are usually to nice for the grade XF VF coins.
4) Polished coins will have marks from polishing, you can see it under jewelers mag. glass very easy.
5) Gold cleaned coins will developed thin film layer.
This is usual practice sellers on ebay to make a coin nicer to sell for higher price. (From my 8 gold coins I bought 6 was cleaned)