I'm not sure this makes this whole thing more fishy, but there are 3 different addresses associated with this company. Dallas TX being the only part that remains consistent.
The address on the receving envelope is:
Credit Approval Dept.
1327 Empire Central DR.
P.O. Box 569799
Dallas, TX 75356-9691
address in their pre-approved letter is:
1327 Empire Central
Dallas, TX 75247
and finally the return envelope address:
P.O. Box 224587
Dallas TX 7522-9271
Now this may have nothing to do with the red flags regarding their offer...just thought I'd point this out.