U mentioned another shop has lower price than theirs, that is the mistake le. i know what you will reply back, but think of it this way. If you said you found $610 for that combo, maybe they will reconsider. By saying out a shop name, you are telling them you have compared prices and if they cant match, you will go to MNC.
Business ethics must change a bit for that shop. Dun directly compare XXX with them. instead, say something like, the lowest you found is $610, but dun say shop name. If they buay gan that shop and they noe u went to their shop 1st, they sure wun give u face.
TP may not have good business ethics, but as long as you get ur items cheaper than the rest, does it matter? Got receipt from them can le.