Help! I Need to Make this Offer As Strong as Possible!

I could really use some help on this one!

 The house that I am working on (I represent the buyers) has an offer on it for $253K with a sale of home contingency.

The sellers have already moved out of this house and have said that they would like to see another offer.  The current listing price is $249,900.  When they received the other offer, the listing price on the house was $259,900.

The house is worth at best $221K according to endless comps that I have run on this house and neighborhood.

My buyers want to get a fair price for the house and want to offer $235K with concessions and allowances of about $20K.  I am hoping that the sellers will be willing to meet us in the middle.

To make the offer more understandable to the sellers, I have enclosed a letter stating all of the reasons that it seems that the house is over priced.  I have backed this up with comps and tax documents. 

The sellers finished out a basement eight years ago without pulling permits.  They have never paid property taxes on this space (900 SF) because of that fact.  Yet they include the 900 SF in the total square footage to be sold. 

Is there anything else I can do to make this offer seem stronger?  I am having my clients put down a substantial amount of earnest money as well. 

I was thinking to maybe revise the offer again before submitting it – I would change all of the items the buyers are asking for (several aesthetic improvements and some closing costs) – to just a certain amount for improvements and then the closing costs, so it doesn't appear that we are asking for too much as WELL as the reduction of the house price.


What do you think?  Any other ideas?