A properly filed lien would prevent you from being able to sell the house without satisfying the lien out of the proceeds, and theoretically could be used to force a sale of the property through a foreclosure proceeding to satisfy the alleged debt (though it is hard to imagine anyone going to all that trouble over $200). There are a number of technical requirements that must be followed in order to place a valid contractor's lien on a property though, and it may be that this lawn service has not and/or cannot meet those technical requirements. You might call up the owner and see if you can work it out.
Georgia's Materialman and Mechanics Lien Law (O.C.G.A. s 44-14-361) provides that someone improving real property by furnishing goods or services may, within 90 days of the last day they furnished services or goods, file a lien to protect their claim for owed amounts. There are very specific requirements for filing and compliance with these requirements are strictly construed by the court. While it is less likely that someone will file for $200 (the preparation cost and filing fees are half that), these costs ARE recoverable if they move forward on the lien and therefore many companies will indeed file for this amount. Once they file, they provide you notice of the lien and then have a year to file suit to "perfect" the lien. Once the lien is perfected, they can foreclose on the property. In the meantime, your lender may respond and notify you that you are in default or it might interfere with a sale on the property or a refinance.
This response is for informational purposes only and may not be deemed to create an attorney client relationship. If you wish to discuss this with one of our construction law attorneys, please contact us in private.