Let's examine this...
FIRST HALF OF THE TRADE
So, you are getting a slight upgrade at your RB1 with this trade. That's how impressive Richardson has been this year: he's just a hair lower than Ray Rice in fantasy value. What he MAY be doing is offering you this trade because the difference in each player's schedule. 3 out of the next 4 weeks Rice has bad match-ups (including playoff weeks), and the 4th is average. Of course, he's still unbenchable, but still. On the other hand, Trent's next 4 weeks are 2 favorable, one average, and one unfavorable.That makes it even less of an upgrade at RB1 for you. Keep that in mind.
SECOND HALF OF THE TRADE
You're taking a major hit at your flex spot. Either taking Demaryius out for Leshoure or Percy Harvin is a significant downgrade. Percy is out this week, and it's not easy to predict his value when he returns, especially given the shaky nature of Christian Ponder's second-half of this season. He'll likely produce, but not Demaryius Thomas-level production. Leshoure has had the hot hand as of late, but I can't trust his consistency moving forward, especially with the ankle issue this week. That's a good side note: you are trading Peyton Manning's favorite target for two hurt guys. A quick look at their schedules for a double-check: Thomas has 2 favorable match-ups and 2 average. Percy has one bad and two average (this week would have been favorable, but he's not playing). Mikel Leshoure (not "Mikle") has 4 average match-ups. Unless you consider Leshoure an upgrade from Thomas, this isn't looking so hot.
This trade leaves your lineup significantly weaker. And just think - he's getting Demaryius Thomas (#5 WR overall) and Trent Richardson (#5 RB overall). He's drooling at this deal. This is a "Make" deal for him, a "break" deal for you, imho. I would absolutely not go for this. I'd suggest a counter, but I think you may have accidentally listed your team twice, instead of his and yours.
Stay strong; you have a solid line-up. I mean, when Demaryius Thomas is your flex, you're doing PRETTY great. (Note my jealousy