It's really variable.
Some brands are very prone to some transfer, like Tolstoi. I don't think I'd consider any premium for a Tolstoi with a light transfer on the front.
For other brands it's less common, and I think for some it's basically unknown.(And that might be because the backs themselves are rare - like Drum or BL460 - And having said that the next poster will probably show one of those with a transfer
)
The other aspect is how strong the transfer is. The ones with very strong transfers are valuable. One of the guys that actually can and does collect them could give you a better idea.
Minor ones might carry some small premium, but rarely do. I have a couple where you can see a mark on the back, then later realize it's a transfer of the players collar or glove or something. Unless it's really clear it's not a big deal
Steve B