The suffix 'monger' means one who deals or trades in something. Apart from the examples you have given, you will see it used to refer to people who trade in particular goods, such as, fishmonger and ironmonger. Not all traders are described this way - while someone who trades in fish is called a fishmonger, someone who trades in meat is not a meatmonger, but a butcher! I should note that the two examples you gave carry a derogatory connotation. Whereas to describe someone as a fishmonger is quite neutral - it merely describes their trade, with no negative connotations attached. I hope that is helpful.

I have just thought of more examples which are in a similar vein to the ones you had: hatemonger, and fearmonger, which I think, is just another way of expressing 'scaremonger''. As you can see, this use of -monger is for a person who spreads negative and undesirable behaviours or feelings. It would never be used in the context of positive outcomes, such as 'peacemonger'.

scandalmonger, alemonger, fashionmonger, newsmonger :)