What kind of amp for my subs?

As mentioned above it's sad but true that some shops are not as knowledgeable as they should be but this "should" be pretty basic for any shop.
Since you mentioned you had a pair of dual 4 ohm subs and you are planning to use the bigger amp that actually does a slightly under rated 700 watts rms @ 4 ohms they need to wire each sub in series for an 8 ohm load and then parallel the subs together for a final 4 ohm load to the amp.