The 22-year-old defender is set to sign a deal which will keep him at the Us – a full-time club which trains three days a week – until the summer of 2016 for an undisclosed fee understood to be between £5,000 and £7,000.
Having seen his stock rise on the back of some dominant performances at Tatnam this season, Spetch courted the interest of several Football League clubs and trialled with Cherries, Portsmouth, AFC Wimbledon and Port Vale.
In the absence of an offer from a professional club, Spetch vowed to focus on his football with Dolphins before Sutton last week swooped in an attempt to boost their own promotion prospects.
But while Killick admitted that handing Spetch an element of control over the transfer would appear controversial to some, he insisted his club felt duty bound to let the player decide his own fate.
The Poole boss told the Daily Echo: “There will be eyebrows raised as to why we are allowing someone who is, arguably, our best player to leave at this stage of the season but people who know the background and personal element to all of this will understand.
“The timing of it was desperately disappointing from our point of view but when Will signed his contract, we always said we would not be obstructive if anyone came in, particularly if it was an offer of full-time football.
“As a club, we were in a difficult position and felt we had to do the right thing by Will and that was how it came about.
“I always said that if Will made it clear he wanted to go, it would make it pretty impossible for us to stand in his way.
"That would not be the case with every contractual situation but as disappointed as we are to lose him, everyone felt it was the right way to conduct things.
“I feel I have always had a great relationship with Will and have a great deal of respect and affection for him. We are all immensely grateful for what he has done for the club and, personally, I hope everything turns out well for him.”
Killick confirmed he would look to draft in another defender to replace Spetch but would not be drawn on the prospect of a return for former Poole captain Michael Walker who is contracted to rivals Weymouth but has been on the transfer list since December.