Caveat emptor
Larger critter tanks are typically made with thinner glass as I recently found when comparing a standard 40B with one with a slotted lid for a screen top. Could be 10s/20s are all the same in terms of glass thickness and that unless/until you get north of 20 gallons they're basically the same in terms of glass thickness but one should not expect good results from filling anything larger that uses thinner glass. Recommend that you measure the glass thickness on the tanks you have and use that for comparison.
None of the tanks in the picture except for what seems to be an overturned 55 need center-bracing as they're too small, but you do not want a 55 with a broken center brace unless you plan on replacing the whole top molding or using it half-filled for a grow-out tank/palidarium.
As for used tanks we've already gone down this road. I have 40 tanks including a 100, 75, 2 55s and 2 40Bs, all used, all trouble-free for 3+ years. I resealed the 100 but then I knew it leaked when I bought it.
With brand spanking-new dedicated aquariums up to 55 gallons selling for a $1/gallon, I do agree there's lot to be said for saving money elsewhere, but then a deal is just that.
Luck.