guest artists

i work in a small studio in ne pennsylvania . we would be interested in having some guest artists come through. my question is; how do they usually go about it, would the artist get payed like he worked for us (standard %)? or do they just give us a small cut? has any one ever heard of the host getting some free work and the artist keeping all the money he makes? is it usually just friends that come to guest spot? or is there any artists that just do it for anyone? any info on this subject would be appreciated. also if anyone reading this would be interested in guest spotting send me a msg and ill send you shop info and all that. thanks in advance p.s. love the site gabe i check it more than my email!!