Main occupational hazard of not buying wax and ripping to build a set you want is you buy mostly picked-through lots from others and then trade for your commons/semi-stars needs here. Sadly, it typically means the last card you need is the monster card from the set. Cases in point:
2001 Topps: https://www.tcdb.com/ViewCard.cfm/sid/1486/cid/280340/2001-Topps-726-Ichiro-Suzuki?PageIndex=8
2006 Topps: https://www.tcdb.com/ViewCard.cfm/sid/1930/cid/207776/2006-Topps-641-Justin-Verlander?PageIndex=7
2011 Bowman, Prospects: https://www.tcdb.com/ViewCard.cfm/sid/57524/cid/2293114/2011-Bowman---Prospects-BP1-Bryce-Harper?PageIndex=1
2013 Topps: https://www.tcdb.com/ViewCard.cfm/sid/61443/cid/4945111/2012-Topps-661-Bryce-Harper?PageIndex=11
And these don't count the four sets where I need 2 cards (1999 Topps T&R, 2011 Topps Update, 2018 Bowman Prospects, 2019 Bowman Prospects), the two sets where I need 3 cards (2018 Topps Update, 2020 Stadium Club), and one set where I need 4 cards (2010 Bowman Prospects)--guess which ones I need and you've got a good chance of being right. Also doesn't count the sets I'm not close on, where I'm sure I'll find new monsters to be missing.
If you've got one of the above that you'd be willing to trade, check my Trade list and hopefully we can work something out. I've already had one trader on here turn down an even value RC for RC trade for one of the above (seem to recall it was because he doesn't trust trading high value cards online, fair enough), so I'm not sure how successful I'd be reaching out to others who have these on their Trade lists. Thanks for listening to my whining, and happy collecting!
P.S. If anyone finds the last card they need for a set on my Trade list, I can almost guarantee we will come to an agreement. I love collecting pelts for finishing others' sets almost as much as I love finishing my own sets.