Secateurs that stop cutting are usually blunt
I once binned a pair of secateurs because they had "stopped cutting". They had not. They had a film of rose sap on the pivot and an edge so rounded it shone. I bought another pair the same week. By June that pair chewed as well. The first ones are still in a drawer. A file would have been enough.
A chewed cut is not a cut. The stem comes away with a ragged stub, the bark peels, and you have to go back and tidy a wound you made. People blame the plant. The plant was fine. The blades were not meeting.
Bypass secateurs work like scissors. Two blades pass each other and the stem is sheared. That is what I want on live green growth. Anvil secateurs have one sharp blade that closes onto a flat block. They mash living tissue. They will shorten dead, dry wood. They will not give you a clean live cut, and I would not buy a pair sold as if they did both jobs the same way.
When they stop cutting I would not buy a new pair until I have checked the old ones. Close the handles and look along the edge. If there is daylight between the blades, or they scissor past without meeting, they will crush. A loose pivot does the same. Tighten the bolt until the blades meet and still open without a grind. If the bolt will not hold a setting, the thread is worn and that pair is finished.
Sap is the cheap failure. After a season of roses or anything sticky, the blades glue themselves half shut. You feel it as stiffness, then as a cut that starts and tears. Wipe them. Put a drop of oil on the pivot. That is the same winter habit I wrote about in Winter tools need a wipe and a film of oil. If the edge is rounded and shiny, that is blunt, not dirty. A small stone or a fine file, drawn along the bevel only, will often bring a decent pair back. I would not grind the flat face of a bypass blade. That face is meant to stay flat so the cut stays clean. Grind it and you have built a wedge that never meets.
Cheap soft metal is the case for replacement. If a light prune of last year's growth rolls the edge, or one woody stem leaves a nick that will not file out, the steel will not hold a sharpen. I have nicked a blade on a hidden tie wire and then kept cutting. Every cut after that was worse. Stop. File the nick out if you can. If you cannot, that pair will snag forever.
I would also check the lock and the handles. A lock that opens in a pocket is a cut waiting. A lock that will not open with wet hands is almost as bad. You will force it. You will nick the blade. Hollow plastic handles that flex when you squeeze are a sign the pivot will walk. I would rather have short, stiff handles I can control than long ones that twist. Length is not leverage if the blades miss.
Skip any pair sold with no steel grade and no spare spring. A loose coil spring that pops out will vanish in the border the first time you open the lock one-handed. I have spent more time on my knees looking for a spring than I have spent cutting. Skip the three-pair garden set in a plastic wallet. Unmatched blades, soft metal, no spare parts. Skip anything described only by colour. I do not need a red pair and a green pair. I need one pair that meets.
This matters all year, but the damage shows when the jobs thicken. In late winter and early spring I want a clean pair for the cuts I wrote about in A spring prune kit is smaller than the catalogues say. In September the jobs change again, and the same pair comes off the hook for September cut-back is a tool choice. A blunt pair in either month tears more than it prunes.
I still oil them after a wet session, not only at the end of the season. Wet sap sets. A pair left shut in a damp shed is a pair you will fight in the morning.
If I later add a buy link here, it will be a paid promo.