Take the cost of the card, plus the grading cost and look at PriceCharting.com or ebay sold listings for comps on what you think the grade will be
Swordsoul has 3 strong Synchro monsters, the main one is Swordsoul Grandmaster - Chixiao that in addition to seeking any card of the archetype to the hand, also has the quick effect of targeting a monster on the field and negating its effects
These types of purchases can be a true treasure trove for collectors
While the "ease of flipping" category is, in large part, a product of the number of defense counters on the battle (battles range from three to seven defense counters, and a battle with three defense counters will be much easier to flip than one with seven), it also takes other factors into consideration, like whether the battle makes creatures (if so, we can use them to help defeat the battle, making it easier to flip) or whether the battle acts as removal (which can get a blocker out of the way, making it easier to attack and defeat the battle)
Shuster 2008, p
That way, it will be locking the opponent for up to 2 turns, rather than 2 times