Fundamentally the price has to be right. Overcharge and you wont get asked back, undercharge and your a fool.
I could put a couple of daft big bills in , get the money but there is no chance of returning. That said we could be sat on our arses at a till in a supermarket chatting up the girls for £6 an hour. Its got its plus points but its still only £6 an hour.
A few quid per mole means, imo
a.) You catch loads of moles and put a whopping bill in and farmer giles isnt happy but pays up.
b.) The month after when one or two pop up you drive over there, set traps, drive back over next