Canaccord Genuity has lowered its rating for estate agents portal Rightmove from 'buy' to 'hold', saying that it sees littles upside after the stock's recent good performance.Since 30 July when the company reports its half-yearly results, the shares have risen 8% to 2,456p, outperforming the market and especially newly-listed rival Zoopla.The broker said that Rightmove generates high-quality returns and the business has good momentum. However, it added: "As the share price rises the value attractions reduce."The recent appreciation in the shares means that Canaccord's 2,600p target price now only represents 6% potential upside.For now, in the absence of any news from Agents' Mutual - a new organisation owned by estate agents hoping to undercut both Rightmove and Zoopla - and its website 'onthemarket.com', Canaccord has left its revenue and earnings forecasts for Rightmove unchanged.However, it warned that estimates could come under pressure if Rightmove's clients support Agents' Mutual's possible launch in 2015.Rightmove's share price was down 1.3% at 2,371p by 12:41 on Tuesday.